Variable-valence metals catalyzed solid NaBiO3 nanosheets for oxidative degradation of norfloxacin, ofloxacin and ciprofloxacin: Efficiency and mechanism

Electron deficient Bi3+δ serves as N2 absorption sites and inhibits carriers recombination to enhance N2 photo-fixation in BiOBr/TiO2 S-scheme heterojunction

Efficient carriers separation and multiple nitrogen (N2) activation sites are essential for N2 photo-fixation. Here, we found that the BiOBr/TiO2 (BBTO) displayed an attractive reversible photochromism (white → grey) due to the generation of electron deficient Bi3+δ, which was produced by the hole trapping of Bi3+ under light irradiation. Interestingly, more Bi3+δ were detected in the BBTO heterojunction than in pure BiOBr, attributing that the hole trapping was promoted by the built-in electric field in the Step scheme (S-scheme) heterojunction. In the BBTO, the electron deficient Bi3+δ enhanced carriers separation and served as the reactive active site to adsorb more N2. Consequently, the BBTO possessed an excellent N2 photo-fixation activity (191 μmol gcat-1 h-1), which was 7.7 and 18 times higher than that of pure BiOBr (24.8 μmol gcat-1 h-1) and TiO2 (10.6 μmol gcat-1 h-1), respectively. Therefore, this work provides a new perspective for enhancing N2 photo-fixation by the electron deficient photocatalysts with S-scheme heterojunction.

Effect of fulvic acid concentration levels on the cleavage of piperazinyl and defluorination of ciprofloxacin photodegradation in ice

Ice is an important physical and chemical sink for various pollutants in cold regions. The photodegradation of emerging fluoroquinolone (FQ) antibiotic contaminants with dissolved organic matter (DOM) in ice remains poorly understood. Here, the photodegradation of ciprofloxacin (CIP) and fulvic acid (FA) in different proportions as representative FQ and DOM in ice were investigated. Results suggested that the photodegradation rate constant of CIP in ice was 1.9 times higher than that in water. When C_FA/C_CIP ≤ 60, promotion was caused by FA sensitization. FA increased the formation rate of cleavage in the piperazine ring and defluorination products. When 60 < C_FA/C_CIP < 650, the effect of FA on CIP changed from promoting to inhibiting. When 650 ≤ C_FA/C_CIP ≤ 2600, inhibition was caused by both quenching effects of 143.9%-51.3% and light screening effects of 0%-48.7%. FA inhibited cleavage in the piperazine ring for CIP by the scavenging reaction intermediate of aniline radical cation in ice. When C_FA/C_CIP > 2600, the light screening effect was greater than the quenching effect. This work provides new insights into how DOM affects the FQ photodegradation with different concentration proportions, which is beneficial for understanding the environmental behaviors of fluorinated pharmaceuticals in cold regions.

Fast photo-Fenton-like oxidation in bismuth catalysis: A novel Fe(III) self-doped sodium bismuthate nanosheet

Sodium bismuthate dihydrate (NaBiO₃.2 H₂O, NBH) nanosheets were successfully prepared in this study using the persulfate oil bath oxidation method. Benefited from the unique layered structure of NBH, the Fe(III) as a variable valence metal ion was explored for enhancing NBH activation of peroxymonosulfate (PMS) to degrade levofloxacin (LVF) in the visible-light catalytic system. Based on results of the reactive oxygen species (ROS) quenching experiments and electron paramagnetic resonance (EPR) analysis, singlet oxygen (¹O₂) and superoxide radical (O₂^·-) were identified as the main ROS. The morphology, chemical structure, and optical properties of NBH were analyzed using various characterization methods. It was confirmed that Fe(III) embedded in the NBH via the ion exchange with Na, resulting in lattice oxygen vacancies on the surface of the NBH, after the formation of oxygen defect sites, reacts with PMS in the solution to produce active oxygen species with oxidizing efficiency. This study expands the technological application of NBH in the catalytic oxidation of variable valence metals, which are essential for the removal of fluoroquinolone antibiotics.

Effects of ciprofloxacin on Eichhornia crassipes phytoremediation performance and physiology under hydroponic conditions

Antibiotics can be absorbed by aquatic plants, but they seriously affect the health of aquatic plants and threaten the steady state of aquatic ecosystem. The phytoremediation performance and physiology of floating macrophyte (Eichhornia crassipes) under antibiotic ciprofloxacin (CIP) hydroponic conditions were investigated. It was found that CIP absorption of E. crassipes was up to 84.38% and the root was the main absorption tissue. Hydrolysis and microbial degradation were the second removal pathway of CIP followed the plant absorption. After 7 days of CIP exposure, the photosynthesis efficiency of E. crassipes remained stable, and the presence of CIP did not inhibit the growth of the plant. On the 14th day, the superoxide dismutase and catalase activities were increased in response to the CIP stress. However, the tender leaves of E. crassipes turned white and shrivel, attributed to a decrease in chlorophyll content and chlorophyll fluorescence parameters after 21 days of CIP exposure. These findings will have significant implications for E. crassipes to absorb CIP on a limited time-scale and provide a phytoremediation technology for antibiotics in water.

Degradation of atrazine in water by Bi2MoO6 and visible light activated Fe3+/peroxymonosulfate coupling system

In this study, the effects of ferric ion (Fe³⁺) on the degradation of atrazine (ATZ) in Bi₂MoO₆/peroxymonosulfate (PMS) system under visible light irradiation was investigated. With the addition of Fe³⁺, ATZ in the visible light/Bi₂MoO₆/PMS system degraded rapidly after 20 min treatment (removal rate > 99%). The enhancement of ATZ removal can be attributed to the role of Fe³⁺. As an electron transfer mediator, Fe³⁺ not only inhibits the recombination of photo-charges and prolongs the life of photogenerated carriers, but also promotes the activation of PMS by accelerating the electron transfer from Bi₂MoO₆ to PMS. The generation of ^•OH and SO₄^•- in the system was determined via electron paramagnetic resonance (EPR) technology and quenching experiments. Furthermore, the characterization of Bi₂MoO₆ before and after reaction, influence of the reaction parameters (i.e., catalyst and PMS dosages, Fe³⁺ and ATZ concentration, initial pH), influence of inorganic anions and humic acid, and the recyclability of catalyst in the vis/Bi₂MoO₆/PMS/Fe³⁺ system was also investigated. Additionally, the existence of Fe³⁺ also exhibits a wide selectivity for the degradation of different pollutants and high treatment efficiency. In general, the vis/Bi₂MoO₆/PMS/Fe³⁺ system demonstrated the potential as an efficient, economical, and environment-friendly water treatment process.

Heterogeneous ozonation of ofloxacin using MnOx -CeOx /γ-Al2 O3 as a catalyst: Performances, degradation kinetics and possible degradation pathways

In this study, the performance of ofloxacin (OFX) degradation in synthetic wastewater using synthesized MnO_x -CeO_x /γ-Al₂ O₃ as a heterogeneous ozonation catalyst was evaluated. The removal rates of OFX and chemical oxygen demand (COD) during 15-day continuous-flow experiments were 98.2% and 76.7% on average, respectively. An ozone index (mgCOD/mgO₃ ) of 1.09 with a high ozone utilization efficiency of 91.39% was achieved. The pseudo-first-order rate constant of ofloxacin degradation reached 15.216 × 10^-2  min^-1 , which was five times that (3.085 × 10^-2  min^-1 ) without catalysts. The results of gas chromatography-mass spectrometry (GC-MS) demonstrated that a variety of small-molecule organics occurred in the final oxidation products, such as 4-hydroxyl-4-methyl-2-pentanone and 2-oxoadipic acid in addition to homologs of OFX. The results of this study suggested that hydroxyl radicals played critical roles in the degradation and mineralization of OFX via four main pathways: (a) electrophilic addition of nitrogen; (b) breakdown of carbon-carbon double bonds; (c) hydrolysis of ether rings; and (d) halodecarboxylation of carboxyl groups. The biodegradability (BOD₅ /COD) of OFX after catalytic ozonation reached 0.54. PRACTITIONER POINTS: Ofloxacin wastewater was treated using catalytic ozonation in a 15-day continuous experiment with MnO_x -CeO_x /γ-Al₂ O₃ as a catalyst. The ozone index reached 1.09 mgCOD/mgO₃ during ozonation of ofloxacin. The presence of the catalyst increased the reaction rate constant by a factor of five. 4-hydroxy-4-methyl-2-pentanone was the primary ofloxacin oxidation product.

Effects of natural colloidal particles derived from a shallow lake on the photodegradation of ofloxacin and ciprofloxacin

Natural colloidal particles (NCPs), which are ubiquitous and abundant in surface waters, may play a crucial role in the sunlight-driven transformation of organic contaminants. This research focused on the effects of NCPs on the photodegradation of two fluoroquinolone antibiotics (FQs), ofloxacin (OFL) and ciprofloxacin (CIP), and assessed the photosensitivity of colloidal organic matter (COM). Results showed that the photodegradation rate constants (k_obs) of OFL and CIP in NCP solutions ranged from 9.28 × 10^-2 h^-1 to 15.98 × 10^-2 h^-1 and 63.88 × 10^-2 h^-1 to 196.59 × 10^-2 h^-1, respectively, and NCPs can significantly accelerate the photodegradation rate of OFL and CIP. Indirect photodegradation (IP) accounted for >50% of the overall observed degradation in most treatments and was the dominant degradation pathway for the two FQs, especially for CIP, for which IP reached 82%-94%. In the IP process, the contributions of triplet states of colloidal organic matter (³COM^⁎) to the photolysis of OFL and CIP were close to 42% and 46%, respectively. The compositions of COM played an important role in the IP of the FQs, among which terrestrial sources of COM tended to have higher photoreactivity than biological sources. This study is essential in predicting the photochemical effect of FQs and also allows for a better understanding of the real environmental fate of antibiotic contaminants.

Dark formation of reactive oxygen species by bifunctional copper doped sodium bismuthate: Direct oxidation vs catalytic oxidation of organic pollutants

Sustained generation of reactive oxygen species for aquatic decontamination is desired, but the strategies aiming at this goal usually involve tremendous input of chemicals or energy, which for practical purpose have hindered their implementation. Here we propose a very simple approach for degrading organic pollutants based on copper doped sodium bismuthate (CSB), in which reactive oxygen species can be continuously generated requiring no irradiation or other chemicals. The material was easily prepared by coprecipitation of NaBiO₃·nH₂O and Cu(NO₃)₂. Two stages of cyclic degradation of organic pollutant in sequence by the same CSB powder, alone with series of characterization measurements and control experiments were designed. CSB mediated reaction proceeds via two distinct mechanisms viz. direct oxidation and catalytic oxidation, each involving different primary reactive species and resulting in different product profiles. Direct oxidation occurs accompanied by the structural transformation of CSB involving singlet oxygen, originated from lattice oxygen, as the responsible species, while catalytic oxidation employs dissolved oxygen to primarily yield superoxide radical owing to the presence of oxygen vacancy. Our findings provide novel insights into the direct and catalytic oxidative activity of CSB, and suggest a based-on approach for simple, efficient and sustained generation of reactive species for water treatment.