One-pot hydrothermal synthesis of Bi2O3-WO3 p-n heterojunction film for photoelectrocatalytic degradation of norfloxacin

Fluoroquinolone antibiotics in the aquatic environment: environmental distribution, the research status and eco-toxicity

The increasing presence of fluoroquinolone (FQ) antibiotics in aquatic environments is a growing concern due to their widespread use, negatively impacting aquatic organisms. This paper provides an overview of the environmental distribution, sources, fate, and both single and mixed toxicity of FQ antibiotics in aquatic environments. It also examines the accumulation of FQ antibiotics in aquatic organisms and their transfer into the human body through the food chain. The study identifies critical factors such as metabolism characteristics, physiochemical characteristics, light, temperature, dissolved oxygen, and environmental compatibility that influence the presence of FQ antibiotics in aquatic environments. Mixed pollutants of FQ antibiotics pose significant risks to the ecological environment. Additionally, the paper critically discusses advanced treatment technologies designed to remove FQ antibiotics from wastewater, focusing on advanced oxidation processes (AOPs) and electrochemical advanced oxidation processes (EAOPs). The discussion also includes the benefits and limitations of these technologies in degrading FQ antibiotics in wastewater treatment plants. The paper concludes by proposing new approaches for regulating and controlling FQ antibiotics to aid in the development of ecological protection measures.

Development of efficient and economic Bi2O3/BN/Co3O4 composite photocatalyst: Degradation mechanism, pathway and toxicity study of norfloxacin

The production of cheap, efficient, and stable photocatalysts for degrading antibiotic contaminants remains challenging. Herein, Bi2O3/boron nitride (BN)/Co3O4 ternary composites were synthesized using the impregnation method. The morphological characteristics, structural features, and photochemical properties of the prepared photocatalysts were investigated via X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and ultraviolet-visible (Vis) diffuse reflectance spectrum techniques. BN was used as a charge transfer bridge in the ternary composites, which afforded a heterojunction between the two semiconductors. The formation of the heterojunction substantially enhanced the charge separation and improved the photocatalyst performance. The degradation activity of the Bi2O3/BN/Co3O4 ternary composites against norfloxacin (NOR) under Vis light irradiation was investigated. The degradation rate of NOR using 5-wt% Bi2O3/BN/Co3O4 reached 98% in 180 min, indicating excellent photocatalytic performance. The ternary composites also exhibited high photostability with a degradation efficiency of 88.4% after five cycles. Hydroxyl radicals (•OH), superoxide radicals (•O2-), and holes (h+) played a synergistic role in the photocatalytic reaction, where h+ and •O2- were more important than •OH. Consequently, seven intermediates and major photocatalytic degradation pathways were identified. Toxicity experiments showed that the toxicity of the degradation solution to Chlorella pyrenoidosa decreased. Finally, the ecotoxicity of NOR and its intermediates were analyzed using the Toxicity Estimation Software Tool, with most intermediates exhibiting low toxicity.

Advancements in electrochemical technologies for the removal of fluoroquinolone antibiotics in wastewater: A review

In recent times, the need to make water safer and cleaner through the elimination of recalcitrant pharmaceutical residues has been the aim of many studies. Fluoroquinolone antibiotics such as ciprofloxacin, norfloxacin, enrofloxacin, and levofloxacin are among the commonly detected pharmaceuticals in wastewater. Since the presence of these pharmaceuticals in water bodies poses serious risks to living organisms, it is vital to adopt effective wastewater treatment techniques for their complete removal. Electrochemical technologies such as photoelectrocatalysis, electro-Fenton, electrocoagulation, and electrochemical oxidation have been established as techniques capable of the complete removal of organics including pharmaceuticals from wastewater. Hence, this review presents discussions on the recent progress (literature within 2018-2022) in the applications of common electrochemical processes for the degradation of fluoroquinolone antibiotics from wastewater. The fundamentals of these processes are highlighted while the results obtained using the processes are critically discussed. Furthermore, the inherent advantages and limitations of these processes in the mineralization of fluoroquinolone antibiotics are clearly emphasized. Additionally, appropriate recommendations are made toward improving electrochemical technologies for the complete removal of these pharmaceuticals with minimal energy consumption. Therefore, this review will serve as a bedrock for future researchers concerned with wastewater treatments to make informed decisions in the selection of suitable electrochemical techniques for the removal of pharmaceuticals from wastewater.

Intrinsic point defects and the n- and p-type dopability in α- and β-Bi2O3 photocatalysts

In this work, all kinds of intrinsic point defects, unintentional N and H impurities and possible complex defects between impurities and native defects in α- and β-Bi₂O₃ with different growth conditions are systematically investigated using hybrid density functional calculations. And then, the n- or p-type doping mechanisms in α- and β-Bi₂O₃ are explored and discussed. It is found that α-Bi₂O₃ presents the n-type conductivity under O-poor conditions. The unintentional H interstitials as the shallow donors should be majorly responsible for the n-type conductivity character. While under O-rich conditions, α-Bi₂O₃ displays the p-type conductivity, and the unintentional complex defects V_Bi1 + 2H as the shallow acceptors should be the primary origins of the p-type conductivity. The hydrogenation of the Bi vacancy in α-Bi₂O₃ not only significantly lowers the formation energy of the Bi vacancy but also markedly decreases its acceptor transition level. This well explains the experimental observation that α-Bi₂O₃ changes from n-type to p-type conductivity with increasing O partial pressure. Compared to α-Bi₂O₃, β-Bi₂O₃ always presents the n-type conductivity behaviour regardless of the growth conditions. The native O1 vacancies (V_O1) and unintentional H interstitials in β-Bi₂O₃ are shallow and excellent donors. They are responsible for the n-type conductivity and further perfectly explain the observed unintentional n-type conductivity character in β-Bi₂O₃ experiments. Understanding the defect physics in α- and β-Bi₂O₃ could inspire more significant studies on developing Bi₂O₃-based photocatalysts.

Exceptional visible-light photoelectrocatalytic activity of dual Z-scheme Bi@BiOI-Bi2O3/C3N4 heterojunction for simultaneous remediation of Cr(VI) and phenol

Developing highly efficient and stable photocatalysts remains a major challenge for the remediation of environmental pollutants. In this work, the Bi⁰ decorated BiOI-Bi₂O₃/C₃N₄ heterojunction (Bi@BiOI-Bi₂O₃/C₃N₄) film was fabricated through ultrasonic stripping, I^- etching and in situ UV-reduction processes and then characterized thoroughly by various analytical techniques. The characteristics of simultaneous mitigation of phenol and Cr(VI) were evaluated over Bi@BiOI-Bi₂O₃/C₃N₄ photoanode under visible light. The results exhibited that both phenol and Cr(VI) were removed completely by the photoanode at 2.5 V within 1.5 h, superior to our previous report. The synergy of the surface plasmon resonance (SPR) effect of Bi⁰ and ternary heterojunction accelerated the separation and transfer of photo-induced charge carrier and thus heavily promoted the removal efficiency. Moreover, the excellent stability of this photoanode was hold with no considerably activity attenuation after 4 cycles. Finally, a dual Z-scheme charge transfer process was presented. This work offers an attractive pathway to construct highly active photoelectrode with promising application for simultaneous remediation of organics and heavy metals in wastewater.

Facile Synthesis of Nano-Flower β-Bi2O3/TiO2 Heterojunction as Photocatalyst for Degradation RhB

Photocatalysis is a hopeful technology to solve various environmental problems, but it is still a technical task to produce large-scale photocatalysts in a simple and sustainable way. Here, nano-flower β-Bi₂O₃/TiO₂ composites were prepared via a facile solvothermal method, and the photocatalytic performances of β-Bi₂O₃/TiO₂ composites with different Bi/Ti molar ratios were studied. The nano-flower Bi₂O₃/TiO₂ composites were studied by SEM, XRD, XPS, BET, and PL. The PL result proved that the construction of staggered heterojunction enhanced the separation efficiency of carriers. The degradation RhB was applied to study the photocatalytic performances of prepared materials. The results showed that the degradation efficiency of RhB increased from 61.2% to 99.6% when the molar ratio of Bi/Ti was 2.1%. It is a mesoporous approach to enhance photocatalytic properties by forming heterojunction in Bi₂O₃/TiO₂ composites, which increases the separation efficiency of the generated carriers and improves photocatalytic properties. The photoactivity of the Bi₂O₃/TiO₂ has no evident changes after the fifth recovery, indicating that the Bi₂O₃/TiO₂ composite has distinguished stability.

The application of photoelectrocatalysis in the degradation of rhodamine B in aqueous solutions: a review

The pollution of the water environment by industrial effluents is an ongoing challenge due to the rate of industrialisation and globalisation. Photoelectrocatalysis (PEC), an electrochemical advanced oxidation process, has proven to be an effective method for removing organics from wastewater. Photoelectrocatalysis is environmentally benign, cost-effective and easy to operate. In this present review, we examine the recent progress in the removal of rhodamine B dye, a common constituent of textile effluent released into the environment, through photoelectrocatalytic degradation. We present a detailed discussion on the use of different kinds of unmodified and modified photoanodes that have been explored for the photoelectrocatalytic removal of this dye. More importantly, discussions are presented on the mechanisms and kinetics of the degradation of rhodamine B dye using these photoanodes. Hence, this review will be beneficial for researchers in developing future projects in the area of wastewater treatments through photoelectrocatalysis.

Plasmon-induced hole-depletion layer on p-n heterojunction for highly efficient photoelectrochemical water splitting

The photoelectrocatalytic (PEC) water splitting efficiency of semiconductor photoelectrodes is mainly limited by the effective separation and transfer of photogenerated charges. Zinc indium sulfide-cuprous oxide (ZnIn₂S₄-Cu₂O) p-n heterojunction is constructed to enhance the PEC properties of ZnIn₂S₄. The nickel hydroxide iron oxide (NiFeOOH) layer on the surface of the heterojunction can be used as a hole depletion layer under the induction of plasmon resonance of the most surface silver (Ag) (the holes transferred from Cu₂O valence band to NiFeOOH layer can be excited by Ag to produce hot electron consumption, which makes the last remaining hot holes participate in the water oxidation reaction) to further promote the carrier separation and transfer. The results exhibit that ZnIn₂S₄/Cu₂O/NiFeOOH/Ag photoelectrode with dramatically enhanced photocurrent density of 1.22 mA/cm² at 1.23 V versus the reversible hydrogen electrode (V_RHE), which is 9.4 times higher than the pure ZnIn₂S₄. This work provides a promising concept to design photoelectrodes efficiently in PEC water splitting.

Recent development on core-shell photo(electro)catalysts for elimination of organic compounds from pharmaceutical wastewater

Pharmaceutical organics are a vital milestone in contemporary human research since they treat various diseases and improve the quality of human life. However, these organic compounds are considered one of the major environmental hazards after the conception, along with the massive rise in antimicrobial resistance (AMR) in an ecosystem. There are various biological and catalytic technologies existed to eliminate these organics in aqueous system with their limitation. Advanced Oxidation processes (AOPs) are used to decompose these pharmaceutical organic compounds in the wastewater by generating reactive species with high oxidation potential. This review focused various photocatalysts, and photocatalytic oxidation processes, especially core-shell materials for photo (electro)catalytic application in pharmaceutical wastewater decomposition. Moreover, we discussed in details about the design and recent developments of core shell catalysts and comparison for photocatalytic, electrocatalytic and photo electrocatalytic applications in pharmaceutical wastewater treatment. In addition, the mixture of inorganic and organic core-shell materials, and metal-organic framework-based core-shell catalysts discussed in detail for antibiotic degradation.

Visible light-driven photoelectrocatalysis for simultaneous removal of oxytetracycline and Cu (II) based on plasmonic Bi/Bi2O3/TiO2 nanotubes

A visible light-driven photoelectrocatalytic system was constructed based on Bi/Bi₂O₃/TiO₂ nanotubes (NTs) to treat wastewater containing oxytetracycline and Cu²⁺ mixed pollutants. The surface morphology, crystal phase, elemental composition, light absorption property and photoelectrochemical activity of the synthesized Bi/Bi₂O₃/TiO₂ NTs were investigated. The composite film, Bi/Bi₂O₃/TiO₂ NTs was used for the photoelectrochemical removal of oxytetracycline, and it had excellent visible light photoelectrocatalytic performance. Under optimal conditions, the composite film was simultaneously used to remove coexisting oxytetracycline-Cu²⁺. The study results show that the reduction of Cu²⁺ on cathode was promoted by oxytetracycline while the degradation of oxytetracycline on photoanode was slightly suppressed by Cu²⁺. Also, possible photoelectrocatalytic degradation pathways for oxytetracycline-Cu²⁺ were analyzed by HPLC-MS.

Photoelectrocatalytic degradation of deoxynivalenol on CuO-Cu2O/WO3 ternary film: Mechanism and reaction pathways

A ternary film of CuO-Cu₂O/WO₃ possessing high visible-light photoelectrocatalytic (PEC) performance was prepared for degradation of deoxynivalenol (DON). In such a ternary film, the introduction of CuO-Cu₂O significantly promoted the absorption of WO₃ in the visible region and reduced the recombination of photogenerated charge carriers. As a result, the CuO-Cu₂O/WO₃ film exhibited high photoelectrochemical activity under visible light illumination. The PEC performance of CuO-Cu₂O/WO₃ film was evaluated by the decoloration of Rhodamine B. The result indicated that the CuO-Cu₂O/WO₃ film exhibited higher PEC activity than WO₃ or CuO-Cu₂O film. When the CuO-Cu₂O/WO₃ film was applied to study the removal of DON, the degradation efficiency reached 87.6% after 180-min PEC treatment. According to reactive oxygen species detected by electron spin resonance analysis, a Z-scheme and type-II PEC mechanism was proposed for this ternary film. Furthermore, the intermediates formed during the PEC degradation process of DON were separated by high-performance liquid chromatography and identified with liquid chromatography-mass spectrometry. On the basis of sixteen intermediate products identified, we proposed a degradation pathway for DON in such a PEC system.

Simultaneous removal of organic pollutants and heavy metals in wastewater by photoelectrocatalysis: A review

As a powerful technique by combining photocatalysis with electrochemistry, photoelectrocatalysis has been extensively explored to simultaneously remove mixed pollutants of organic and heavy metal in wastewater in the past decade. In the photoelectrocatalytic system, the bias potential can remarkably promote the oxidation of organic pollutants on the photoanode by suppressing the recombination of photogenerated electron-hole pairs and extending the lifetime of photogenerated holes. Meanwhile, some photogenerated electrons are driven by the bias potential to the cathode to reduce heavy metals. In this review, we summarize the research advances in photoelectrocatalytic treatment of organic-heavy metal mixed pollution systems under UV light, visible light and sunlight. We demonstrate the main operation variables affecting the photoelectrocatalytic removal processes of organic pollutants and heavy metals. The problems for utilization of solar energy in photoelectrocatalysis are discussed. Finally, this review proposes the perspectives for future development of photoelectrocatalysis to industrial applications.

Boosting photoresposive ability of WO3-Bi2O3nanocomposite rods via annealing-induced intrinsic precipitation of nanosized Bi particles

In this study, Bi-particle-functionalized tungsten trioxide-bismuth oxide (WO₃-Bi₂O₃) composite nanorods were prepared by integrating sputtering and hydrothermal syntheses with an appropriate postannealing procedure to induce Bi particle precipitation. Unlike other routes in which metal particle decoration is achieved externally, in this study, photoresponsive one-dimensional WO₃-Bi₂O₃composite nanorods were decorated with Bi particles by using the internal precipitation method. Structural analysis revealed that the Bi-metal-particle-functionalized WO₃-Bi₂O₃composite nanorods with particle size ranging from 5 to 10 nm were formed through hydrogen gas annealing at an optimal annealing temperature of 350 °C. Compared with the pristine WO₃nanorod template, the Bi-WO₃-Bi₂O₃composite nanorods exhibited higher photoresponsive performance, substantial photogenerated charge transfer ability, and efficient separation of photogenerated electron-hole pairs. The study results indicated that the Bi-WO₃-Bi₂O₃composite nanorods had superior decontamination ability and excellent stability toward RhB dye as compared with pristine WO₃. Moreover, the photogenerated charge separation and migration efficiencies of the WO₃-Bi₂O₃nanorods could be tuned through appropriate reduction of the surface oxide layer; this is a promising approach to designing WO₃-Bi₂O₃nanorods with high photoactive performance.

Photoelectrocatalytic reactor improvement towards oil-in-water emulsion degradation

Oil-in-water (O/W) emulsion is critical wastewater that is challenging to eliminate and requires a long treatment process, and it is necessary to develop highly effective removal methods before releasing it into natural water sources. This research has selected the photoelectrocatalytic (PEC) technique to solve this problem by developing a PEC reactor for high efficiency in O/W degradation and understanding the essential factors related to the PEC reactor's efficiency improvement. The PEC reactor has been designed on a large scale with suitable positioning of an electrode that is, designing a light source near the anode electrode to enhance light irradiation efficiency and including a circulating pump to provide continuous flow to the solution through the electrode surface. We studied the main factors of supporting the electrolyte, electrode characteristics, and catalytic process. We investigated the O/W-degradation efficiency using a UV/Vis spectrophotometer, chemical oxygen demand (COD) measurement, and GC-MS analysis. We optimized the PEC reactor using the developed BiVO₄ photoanodes and placed them parallel with the zinc plates. Then, we controlled the applied potential at 1.0 V in 0.1 M Na₂SO₄ supporting an electrolyte under visible light irradiation. The developed PEC reactor can be degraded in the O/W emulsion up to 76% and decreased the COD value up to 78% for 7h. This PEC cell can be completely decomposed of many functional groups, such as carbonyl, ester, nitrile, amine, phosphate, chloro group, and nitro group, that were contained in the O/W substance. The highlight of this research is the designed light source and circulating pump inside of the PEC reactor to enhance the light irradiation, refresh the anode electrode, and understand the critical factor for the improvement of O/W-degradation efficiency. This PEC reactor presents a high-efficiency O/W degradation with practical use and a fast process suitable for further application in high turbidity of wastewater treatment from the oil industry.

Tailoring the Surface Properties of Bi2O2NCN by in Situ Activation for Augmented Photoelectrochemical Water Oxidation on WO3 and CuWO4 Heterojunction Photoanodes

Bismuth(III) oxide-carbodiimide (Bi₂O₂NCN) has been recently discovered as a novel mixed-anion semiconductor, which is structurally related to bismuth oxides and oxysulfides. Given the structural versatility of these layered structures, we investigated the unexplored photochemical properties of the target compound for photoelectrochemical (PEC) water oxidation. Although Bi₂O₂NCN does not generate a noticeable photocurrent as a single photoabsorber, the fabrication of heterojunctions with the WO₃ thin film electrode shows an upsurge of current density from 0.9 to 1.1 mA cm^–2 at 1.23 V vs reversible hydrogen electrode (RHE) under 1 sun (AM 1.5G) illumination in phosphate electrolyte (pH 7.0). Mechanistic analysis and structural analysis using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (STEM EDX) indicate that Bi₂O₂NCN transforms during operating conditions in situ to a core–shell structure Bi₂O₂NCN/BiPO₄. When compared to WO₃/BiPO₄, the in situ electrolyte-activated WO₃/Bi₂O₂NCN photoanode shows a higher photocurrent density due to superior charge separation across the oxide/oxide-carbodiimide interface layer. Changing the electrolyte from phosphate to sulfate results in a lower photocurrent and shows that the electrolyte determines the surface chemistry and mediates the PEC activity of the metal oxide-carbodiimide. A similar trend could be observed for CuWO₄ thin film photoanodes. These results show the potential of metal oxide-carbodiimides as relatively novel representatives of mixed-anion compounds and shed light on the importance of the control over the surface chemistry to enable the in situ activation.

Phosphate electrolyte activates the metal oxide−Bi₂O₂NCN heterojunction.

Growth temperature-dependent phase evolution and photoactivities of sputtering-deposited crystalline Bi2O3 thin films

Crystalline Bi₂O₃ thin films were grown through radio-frequency magnetron sputtering deposition using a bismuth metal target in an Ar/O₂ mixed atmosphere and in an Ar atmosphere with further post-annealing procedures in ambient air.