Degradation Pathways Of Ciprofloxacin Research Articles

Studies on photocatalytic removal of antibiotics, ciprofloxacin and sulfamethoxazole, by Fe3O4-ZnO-Chitosan/Alginate nanocomposite in aqueous systems

An ultraviolet-light-induced antibiotic degradation system based on nano-ZnO and Fe3O4 and chitosan/alginate nanocomposite bead assembly has been developed using a facile green-synthesis approach. In this study Camellia sinensis extract was used as reducing agent to facilitate the formation of the nanoparticles. The Fe3O4-ZnO-CS/SA nanocomposite was employed to degrade ciprofloxacin (CIP) and sulfamethoxazole (SMX) under UV-C light irradiation, and 94.77% and 93.31% degradation was achieved respectively within 180 min with the optimized conditions [pH of 4.0, antibiotic concentration of 10 mg/L, and Fe3O4-ZnO-CS/SA nanocomposite weight of 10 g and 15 g for CIP and SMX respectively]. For both the antibiotics, the pseudo-first-order model fitted well with the reaction kinetics data, while the Langmuir isotherm model showed a better fit compared to the Freundlich and Temkin models. Analyzing various characterization data reaction mechanism for CIP and SMX degradation was proposed. In addition, possible degradation pathways of CIP and SMX were proposed based on the intermediates detected by HR-LCMS analysis. Furthermore, the trapping experiments showed that superoxide (1O2) and hydroxyl (OH) radicals play major role in the photodegradation of CIP and SMX. The effects of ionic strength, natural organics and various natural water systems on degradation efficacy was investigated. The degraded products were found to show less toxicity to a model organism, a fresh water alga, compared to the parent compounds. This work provides a simple strategy to integrate CS/SA with nano-ZnO and Fe3O4 to construct effective nanocomposite photocatalyst for the degradation of different classes of antibiotics.

Step-doped disulfide vacancies and functional groups synergistically enhance photocatalytic activity of S-scheme Cu3SnS4/L-BiOBr towards ciprofloxacin degradation.

Development of efficient photocatalysts for efficient recalcitrant organic pollutants degradation is of great significance. Herein, the step-doped disulfide vacancies S-scheme Cu3SnS4/L-BiOBr (CTS/L-BiOBr) heterojunction photocatalyst was prepared for ciprofloxacin (CIP) degradation. X-ray photoelectron spectroscopy (XPS) analysis, ultraviolet photo-electron spectroscopy (UPS) analysis, band structure and dominant radicals' identification together verified that the transfer of photogenerated carriers conformed to the S-scheme mechanism. Benefited from the interfacial electric field (IEF) of the S-scheme heterojunction and incorporation of L-cysteine with introducing S-vacancies and surface functional groups (-NH2, -COO-), photogenerated charges generation and separation of the CTS/L-BiOBr(10) were greatly improved. With ·OH and h+ as dominant reactive species, CIP removal reached 93% using CTS/L-BiOBr(10) within 180min of visible light irradiation, which was 3.5 times and 2.6 times of pristine Cu3SnS4 and L-BiOBr, respectively. Moreover, possible CIP degradation pathways were proposed and the degradation intermediates ecotoxicity were evaluated. This study could provide reference for designing efficient S-scheme photocatalysts for recalcitrant wastewater treatment.

Overpotential regulation of vanadium-doped chitosan carbon aerogel cathode promotes heterogeneous electro-Fenton degradation efficiency

This work aimed at exploring the effect of optimal overpotential discrepancy between two-electron oxygen reduction reaction (OP2eORR) and metal reduction reaction (OPMRR) of the cathode on electro-Fenton (EF) system performance, and proposing strategy to eliminate overpotential discrepancy. Therefore, series of vanadium-doped chitosan carbon aerogel (xCCA-V) cathodes were fabricated by controlling graphitization degree. With carbonized temperature of 900 °C, the OP2eORR of the 900CCA-V was −0.5 V vs. SCE, the same with the OP for vanadium reduction reaction (OPVRR). This identical OP of the 900CCA-V endowed excellent EF performance, with ciprofloxacin removal of 98.1%, and TOC removal significantly increased by 41.8% compared with Ferrum-doped CCA (900CCA-Fe). Density functional theory calculation revealed efficient active sites for H2O2 adsorption on the 900CCA-V surface. Degradation pathways of ciprofloxacin and intermediates toxicity were determined. This work provides inspiration for developing strategy for overpotential regulation and design novel and efficient cathodes for enhancing EF performance.

Adsorption and oxidation of ciprofloxacin by a novel layered double hydroxides modified sludge biochar

In this study, biochar derived from municipal sludge (SBC) was modified by CoFe-Layered double hydroxides (CoFe-LDH), and used as adsorbent and oxidant for the removal of ciprofloxacin (CIP) for the first time. Under the optimal conditions, the CIP removal rate is increased by 24% compared with the single SBC, while the removal rates of total organic carbon and total nitrogen in the modified one are increased by 24% and 27%, respectively. Mechanism investigation suggested that the specific surface area and adsorption sites of modified biochar increased, and more CIP was adsorbed to the composite surface and then oxidized by more environmental persistent free radicals contained in the CoFe-LDH@SBC, when the adsorbed CIP molecules was oxidized and degraded, the adsorption sites can be freed and thus new CIP could be adsorbed to the CoFe-LDH@SBC. In addition, the plausible degradation pathways of CIP were proposed according to high-performance liquid chromatography-mass spectrometry and density functional theory calculation. It not only reveals that CoFe-LDH@SBC has the high ability of adsorption and oxidation for CIP removal but also sheds novel insight into the application of biochar.

α-(Fe, Cu)OOH/RGO nanocomposites for heterogeneous photo-Fenton-like degradation of ciprofloxacin under visible light irradiation.

Ciprofloxacin (CIP) is a third-generation fluoroquinolones (FQs) antibiotic, and the occurrence of CIP in the water environment has raised growing concerns owning to its environmental toxicity. In this paper, a novel α-(Fe, Cu)OOH/RGO nanocomposite was synthesized via a one-step reflux method for CIP degradation through a photo-Fenton-like process. When the RGO content was 1 wt%, CIP degradation ratio by the α-(Fe, Cu)OOH/RGO nanocomposite reached 100% under visible light irradiation within 120 min, and total organic carbon (TOC) removal ratio reached 60% within 180 min. The result of molecular fluorescence spectra highlighted that the loading of RGO on the α-(Fe, Cu)OOH significantly increased the content of hydroxyl radicals (·OH) in the heterogeneous photo-Fenton-like system and simultaneously inhibited the recombination of photogenerated electron and hole, which played critical roles in the enhancement of CIP degradation. In addition, 11 main intermediates were identified as the degradation products of CIP in the α-(Fe, Cu)OOH/RGO/H2O2/visible light reaction systems using liquid chromatograph-mass spectrometer (LC-MS) analyses. The results demonstrated that three degradation pathways for CIP removal by α-(Fe, Cu)OOH/RGO nanocomposite occurred, including (i) oxidation on the piperazine ring and dealkylation, (ii) defluorination and decarboxylation, and (iii) hydroxylation on the quinolone ring. This work would provide a novel insight of CIP degradation pathways in photo-Fenton-like processes.

Facile construction of Z-scheme Fe-MOF@BiOBr/M−CN heterojunction for efficient degradation of ciprofloxacin

A novel Fe-MOF@BiOBr/M−CN photocatalyst is synthesized via one-pot EG (ethylene glyco)-assisted solvothermal heating. The morphology, microstructure, and composition of the prepared catalysts are characterized by SEM, XRD, FTIR, and XPS. The Fe-MOF@BiOBr/M−CN photocatalyst exhibites better pollutant adsorption and degradation than pure BiOBr. After grafting iron-based metal–organic framework (Fe-MOF) and modified g-C3N4 (M−CN) species, photogenerated electrons can be transferred from BiOBr to M−CN and Fe-MOF species via interfacial charge transfer. Therefore, the separation efficiency of electrons (e−) and holes (h+) is enhanced. Fe-MOF@BiOBr/M−CN−50 can degrade approximately 93% of ciprofloxacin in 120 min under visible light illumination, which is 7.9 and 1.2 times that of pure g-C3N4 (11.8%) and BiOBr (77.4%), respectively. Furthermore, radical capturing experiments and ESR analysis reveal that h+ and ·O2− are the main reactive species in the system. A combination of DFT calculations and radical trapping experiments show that M−CN and BiOBr form a Z-type heterojunction. In addition, Fe-MOF plays a vital role as a carrier acceptor for electron transport. Finally, the degradation pathway of ciprofloxacin is revealed by gas-chromatography–mass-spectroscopy analysis. This study provides new insights into the photocatalytic degradation of pollutants in water.

Three-dimensional electro-Fenton degradation of ciprofloxacin catalyzed by CuO doped red mud particle electrodes: Influencing factors, possible degradation pathways and energy consumption

In this work, CuO doped red mud (CuO/URM) as particle electrode was applied in three-dimensional electro-Fenton (3D/EF) system for ciprofloxacin (CIP) degradation. The operating conditions of CuO/URM dosage, initial pH, applied voltage and aeration intensity were investigated in detail. The optimum degradation efficiency of CIP about 80.66% were achieved after 80 min treatment with CuO/URM dosage of 4 g/3 L, initial pH of 7, applied voltage of 10 V and aeration intensity of 5 L/min. Moreover, the effect of inorganic anions on the degradation of CIP was investigated, and it was found that Cl- promoted the degradation of CIP, while the NO3-, HCO3-, and H2PO4- had an inhibitory effect on CIP degradation. Based on the analysis of UV-Visible spectrophotometer (UV–vis) and liquid chromatograph-mass spectrometer (LC-MS), the degradation intermediates and degradation pathway of CIP in the 3D/EF system catalyzed by CuO/URM particle electrodes were proposed. Compared with the two-dimensional electrochemical (2D/E) system, 3D/EF system had more excellent removal capability of CIP and higher power energy utilization efficiency. The CuO/URM electrodes before and after use were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR). It was proved that CuO/URM exhibited excellent stability. All results demonstrated that the 3D/EF system catalyzed by CuO/URM particle electrodes is a reliable technology for the disposal of CIP wastewater.

Insights into highly effective catalytic persulfate activation on oxygen-functionalized mesoporous carbon for ciprofloxacin degradation.

Nanocarbons have been demonstrated as promising carbon catalysts for substituting metal-based catalysts for the green treatment of wastewater. In this study, oxygen-functionalized mesoporous carbon (OCMK-3) was prepared by wet oxidation and exhibited high catalytic performance against ciprofloxacin (CIP) by activation of persulfate. The effects of environmental parameters (pH, temperature, coexisting ions) and process parameters (temperature, sodium persulfate concentration, catalyst agent dosage, initial concentration) on the removal of CIP were investigated. Compared with the pristine ordered mesoporous carbon (CMK-3), the removal efficiency of CIP by OCMK-3 was increased by 32% under optimal conditions. This rise in activity was attributed to the increase in oxygen-containing functional groups, porosity, and specific surface area of OCMK-3 with improved structural defects and electron transfer efficiency. Furthermore, based on active species scavenging experiments, a dual-pathway mechanism of the radical and nonradical pathways was discovered. The rational degradation pathway of CIP was investigated based on liquid chromatography-mass spectrometry (LC-MS). In addition, the OCMK-3/PS system exhibited high decomposition efficiency in pharmaceutical wastewater treatment. This study provides an in-depth mechanism for the degradation of organic pollutants by carbon-based PS-AOPs and provides theoretical support for further studies.

Efficient removal of ciprofloxacin by heterogeneous electro-Fenton using natural air–cathode

• A novel OCNTs/FeOCl natural air diffusion electrode (NADE) was developed. • OCNTs/FeOCl NADE was applied in a heterogeneous electro-Fenton (hetero-EF) system. • H 2 O 2 was electro-generated without external aeration and activated in situ. • Efficient ciprofloxacin removal was achieved at a wide range of pH (3–9). • The possible mechanism in hetero-EF process with OCNTs/FeOCl NADE was proposed. In this study, we developed a Heterogeneous Electro-Fenton (Hetero-EF) system using an oxidized carbon nanotubes/iron oxychloride natural air diffusion electrode (OCNTs/FeOCl NADE) as the cathode, enabling simultaneous processes of O 2 diffusion, H 2 O 2 electro-generation and the activation in liquid–gas-solid three-phase interfaces on the cathode. Experimental results showed that rapid ciprofloxacin (CIP) degradation was realized over a wide pH range (3–9). CIP was completely degraded in 90 min, with the total organic carbon (TOC) removal efficiency of 46.8% ± 1.9% under the condition of current 75 mA and initial pH 7. The electron paramagnetic resonance and radical quenching experiments revealed that the reactive species of ·OH, ·O 2 – and 1 O 2 were all involved in the process, with 1 O 2 being the dominant contributor in CIP degradation. From the Fukui function based on the theoretical calculation and the degradation intermediates detected by LC-MS, the possible CIP degradation pathways were deduced. The toxicities of CIP degradation products were also predicted. This study demonstrated the feasibility of a simple and cost-effective integrated cathode combining the OCNTs/FeOCl catalyst exhibiting dual Fenton-like and oxygen reduction reaction (ORR) activity with the natural air diffusion electrode in a Hetero-EF system for efficient wastewater treatment.

Carbon defects in biochar facilitated nitrogen doping: The significant role of pyridinic nitrogen in peroxymonosulfate activation and ciprofloxacin degradation

Nitrogen (N) doping endows biochar with remarkable catalytic ability to activate peroxysulfate for degradation of organics. Herein, a new strategy was proposed by creating defective carbon in pinewood-derived biochar (BC800) under alkaline conditions to favor C-N configuration using 2-methylimidazole as an extrinsic N-dopant. After doping process, N presented as pyridinic N (48.5%), pyrrolic N (25.1%), and graphitic N (26.4%) in N-doped biochar (NKBC800) as per X-ray photoelectron spectroscopy (XPS). NKBC800 had a larger specific surface area (1398 m2 g−1), higher defective degree (ID/IG = 0.78), and more active N species, which facilitated peroxymonosulfate (PMS) activation performance. The removal of ciprofloxacin (CIP) was examined by BC800, NKBC800, and alkaline activated biochar (KBC800). As expected, the CIP (30 mg L−1) removal efficiency by NKBC800 (0.2 g L−1) was increased to 87%, five times greater than BC800. In contrast, KBC800 was less efficient in CIP removal (80%) with compromised degradation rate constant. Based on electron paramagnetic resonance (EPR), the degradation mechanisms comprised radical pathway (sulfate and hydroxyl radicals) and main non-radical pathway (singlet oxygen 1O2 and direct electron transfer). Degradation intermediates were recognized with UPLC-MS analysis and main possible CIP degradation pathways was proposed as cleavage of the piperazine ring attributing to 1O2 followed by the substitution of hydroxyl groups. The as-prepared NKBC800 showed good reusability even with consecutive runs and excellent pH stability between 3 and 9. These findings highlighted preparation of metal-free catalyst based on N-doped carbonaceous material with excellent PMS activation ability to remove different classes of antibiotics from wastewater.

Photocatalysis activation of peroxydisulfate over oxygen vacancies-rich mixed metal oxide derived from red mud-based layered double hydroxide for ciprofloxacin degradation

In this work, a low-cost and oxygen vacancies (OVs) enriched mixed metal oxide (M−RM/MMO) derived from red mud-based layered double hydroxide (M−RM/LDH) was applied as an efficient peroxydisulfate (PDS) activator to realize the degradation of ciprofloxacin (CIP) under visible light (VL) irradiation. The optimal composite of M−RM/MMO-700 exhibited good performance, and approximately 87.4% of CIP (10 mg/L) could be degraded at 60 min via the photocatalysis activation of PDS (1.0 mM) over M−RM/MMO-700 (0.2 g/L). The result indicated the abundant OVs in M−RM/MMO-700 could improve light absorption and promote electron-hole separation, both of which were favorable for the activation of PDS, resulting in promoting the generation of active species in M−RM/MMO-700/PDS/VL system. Quenching experiments and EPR technology indicated that O2−, 1O2 and h+ were the main active species for the degradation of CIP. The M−RM/MMO catalyst possessed excellent reusability, stability and magnetic behavior in use. The degradation pathways of CIP were deduced based on DFT calculation and LC-MS analysis. Based on the quantitative structure–activity relationship (QSAR), the ecotoxicity of the degradation intermediates was analyzed in detail. This work provided a new insight for future designing of red mud-based LDHs-derived MMO heterogeneous catalyst with abundant OVs to efficiently treat antibiotics wastewater via the photocatalysis activation of PDS.

Enhanced ciprofloxacin degradation by electrochemical activation of persulfate using iron decorated carbon membrane cathode: Promoting direct single electron transfer to produce 1O2

In this work, electrochemical activation of persulfate (E-PS) for the energy efficient treatment of ciprofloxacin (CIP) was performed using a novel iron-decorated carbon membrane (FeCM) cathode and SnO2-Bi/Ti anode. Synergistic effect of electrochemical oxidation and PS activation resulted in superior CIP removal. The FeCM cathode outperforms various cathodes (Pt, Ti, graphite, and stainless steel), owing to the existence of C = O, Fe2+/Fe3+, and F on FeCM, which can facilitate 1O2 generation and utilization in the E-PS system. Moreover, the continuous supply of negative charges endows rapid redox cycle of Fe2+/Fe3+ on FeCM cathode, which not only prevents iron leaching, but also reduces the consumption of active sites, and thus, enables FeCM with high stability over a wide pH range and improved cyclic performance. The potential of E-FeCM-PS for outdoor application were evaluated by removing various persistent organic pollutants, and treating actual hospital effluent. The CIP removal mechanism in the E-FeCM-PS process and the possible CIP degradation pathways were proposed. Overall, this work provides a plausible route for the continuous production of 1O2 for effective abatement of organic contaminants via electro-activation of PS and gives an insight into the intrinsic role of iron-doped carbon membrane for persulfate cathodic activation.

Facile synthesis of carbon-doped CoMn2O4/Mn3O4 composite catalyst to activate peroxymonosulfate for ciprofloxacin degradation

In this work, carbon-doped CoMn2O4/Mn3O4 (C-CoMnO) composite catalyst were prepared via calcining solvothermal product of Mn2+, Co2+, and 2-methylimidazole in air. The catalytic performance of activating peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation was discussed. The results showed that the 0.1 g L−1C-2CoMnO could effectively activate PMS, resulting in 96.18% CIP was degraded within 60 min. The corresponding total organic carbon removal ratio and apparent rate constant were 81.33% and 0.043 min−1, respectively. The influencing factors, such as Co/Mn molar ratios, calcination temperature, PMS concentration, solution pH, and coexisting ions were explored. The optimal catalytic system exhibited good recycling performance, wide pH adaptation and high resistance to salt interference. SO4⋅−, ⋅OH, and ⋅O2−-based radicals, as well as 1O2 and surface complexes-based nonradicals were participated in CIP degradation. The CIP degradation pathways were proposed. Density functional theory calculations (DFT) indicated that PMS was more easily activated via Co/Mn synergism. The doped carbon was also contributed to PMS activation via facilitating electron transfer. This study may shed light toward the synergistic effect of metal oxides in PMS activation.

Construction and application of BiOCl/Cu-doped Bi2S3 composites for highly efficient photocatalytic degradation of ciprofloxacin

In this work, a novel BiOCl/Cu-doped Bi2S3 photocatalyst was designed to efficiently remove ciprofloxacin (CIP) with high photocatalytical activity and good stability over a wide pH range. Compared with Cu-doped Bi2S3, Bi2S3, BiOCl, BiOCl/Bi2S3, and Cu-doped BiOCl, the photocatalytical degradation rate of CIP (97.1% at 20 mg/L) over BiOCl/Cu-doped Bi2S3 was enhanced by about 84.77, 44.23, 2.95, 2.27, and 1.96 times within 20 min, respectively. Notably, the BiOCl/Cu-doped Bi2S3 photocatalyst also displayed high photocatalytical performance in the degradation of other antibiotics including norfloxacin, ofloxacin, and tetracycline (40 mL, 20 mg/L; 88.3%, 100%, and 95.2% of degradation rate within 30 min, respectively) under visible light irradiation. Radical trapping experiments and electron spin resonance technique indicated that superoxide radicals (•O2−) and photogenerated holes (h+) played crucial roles in the photocatalytic degradation of CIP. Finally, the possible CIP degradation pathways was proposed by detecting the CIP intermediates in photocatalytical reaction process.

Metal-organic framework-derived CuCo/carbon as an efficient magnetic heterogeneous catalyst for persulfate activation and ciprofloxacin degradation

Herein, the authors synthesis an efficient and easily recycled CuCo/C catalyst through one-step carbonization of Cu@Co-MOF-71 (Abbreviated as Cu@Co-MOF in this work) precursor. The prepared CuCo/C has a high degradation efficiency of 90% for ciprofloxacin (CIP) by activating PMS in a wide value of pH 3–9 within 30 min. After pyrolysis, the carbon matrix as a dispersant can promote the highly uniform distribution of active metals. Additionally, the CIP removal efficiency was 85% after four cycles and the catalyst was easily separated from the solution by using magnets, showing the good stability and reusability. To further study the superiority of CuCo/C activated PMS in degrading CIP, the factors such as pH, the dosage of PMS and catalyst, temperature, inorganic ions and pollutant (CIP) concentration were investigated. Furthermore, the Liquid chromatography-mass spectrometry (LC-MS) was utilized to analyze the intermediate products and possible degradation pathways of CIP. Typically, the quenching experiments and electron paramagnetic resonance (EPR) technology were investigated to confirm the main reaction species including SO4▪−, OH▪ and O2▪− radicals as well as nonradical (1O2). This work put forward a simple method for synthesis of metal-organic framework (MOF) derived catalysts and its application in treatment of organic pollutants.

Electrospinning visible light response Bi2MoO6/Ag3PO4 composite photocatalytic nanofibers with enhanced photocatalytic and antibacterial activity

Due to its significant biocompatibility and environmental friendliness, the composite of heterojunction photocatalyst and natural protein is a promising material in the field of photocatalysis. For the first time, direct Z-scheme Bi2MoO6/Ag3PO4 composites with different concentrations of Ag3PO4 were successfully fabricated by an in-situ deposition method, and Bi2MoO6/Ag3PO4@silk fibroin (BMO/APO@SF) films were further constructed by electrospinning technology to explore the photocatalytic activity of heterojunction photocatalysts. The results of various characterizations confirmed that improved photocatalytic performance, including efficient charge separation, and a widened visible light absorption range, could be attributed to the formation of a heterojunction structure between Bi2MoO6 and Ag3PO4, which considerably promoted photocatalytic activity for ciprofloxacin (CIP) degradation. According to the analysis of degradation products measured by Q-TOF, possible CIP degradation pathways were proposed. Density functional theory (DFT) calculation and Laplacian bond order (LBO) analysis were consistent with the results of Q-TOF. Through trapping experiments, the significant contribution of O2– to BMO/APO@SF was demonstrated. Moreover, the antibacterial rates of Bi2MoO6/15Ag3PO4@SF (BMO/15APO@SF) against Escherichia coli and Staphylococcus aureus were greater than 94.36% and 95.72%, respectively, indicating that BMO/15APO@SF had excellent antibacterial performance.

Activation of peroxymonosulfate by iron oxychloride with hydroxylamine for ciprofloxacin degradation and bacterial disinfection

Iron oxychloride (FeOCl) is a known effective iron-based catalyst and has been used in advanced oxidation processes (AOPs). This study intends to achieve more facile free radicals generation from peroxymonosulfate (PMS) activation by exploring the Fe(III)/Fe(II) cycle of FeOCl in the presence of hydroxylamine (HA). With 0.2 g/L FeOCl, 1.5 mM PMS, and 1 mM HA, the PMS/FeOCl/HA system could effectively achieve 98.88% of the oxidative degradation of 5 mg/L ciprofloxacin (CIP) in 15 min and quickly inactivate 99.99% of E. coli (108 CFU/mL) in 5 min at near-neutral pH. HA played an important role in promoting the Fe(III)/Fe(II) cycle, thereby greatly improving the oxidation activity of the system. The reactive oxygen species (ROS) such as HO, SO4− and O2− were identified as the dominated free radicals produced in the system. The intermediate products of CIP detected by liquid chromatograph-mass spectrometer (LC-MS) and three possible degradation pathways of CIP were proposed. The presence of common anions in the PMS/FeOCl/HA system, including HCO3−, Cl−, SO42−, and NO3−, enhanced the degradation efficiency of CIP to varying degrees at the concentrations of 10 mM. Moreover, FeOCl maintained a high degradation capability for CIP after several recycles. This work offers a new promising means of catalyzing the PMS-based AOPs in the degradation of refractory organics.

Hierarchical multi-active component yolk-shell nanoreactors as highly active peroxymonosulfate activator for ciprofloxacin degradation

The reasonable design of the structure and composition of catalysts was essential to improve the catalytic performance of advanced oxidation processes (AOPs). Herein, we reported a simple strategy to synthesize hierarchical Co3O4-C@CoSiOx yolk-shell nanoreactors with multiple active components by using metal–organic frameworks (MOFs). The novel nanoreactors are further used to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. The effects of reaction parameters (pH value, co-existing ions, reaction temperature, etc.) on CIP degradation were systematically investigated. Especially, ∼98.2% of CIP was degraded within 17 min under the optimal conditions, together with the low cobalt leaching and excellent reusability. The appreciable catalytic performance improvement might be due to the synergistic effect of the structure and component design: (1) the hierarchical yolk-shell structure endowed the catalyst with high surface area (∼232.47 m2/g) and fully exposed active sites; (2) abundant highly active ≡Co-OH+ were formed on the surface of CoSiOx; (3) the presence of oxygen vacancies and nitrogen-doped carbon promoted the decomposition of PMS through a non-radical process. The results revealed both the radical (SO4∙-, ∙OH and O2∙-) and non-radical (1O2 and direct charge transfer) should be responsible for the CIP degradation. Moreover, the possible degradation pathways of CIP were proposed through the identification of intermediates using LC-MS/MS techniques and density functional theory (DFT) calculation. Our work highlights that multi-component catalysts derived from MOFs with novel structure have broad application prospects in AOPs.

Peroxymonosulfate activation through 2D/2D Z-scheme CoAl-LDH/BiOBr photocatalyst under visible light for ciprofloxacin degradation

The synergistic effect between photocatalytic and peroxymonosulfate (PMS) activation has been widely applied in the field of sewage treatment. In this work, we synthesized a two-dimensional/two-dimensional (2D/2D) CoAl-LDH/BiOBr Z-scheme photocatalyst via a simple method. Then, multiple detection results demonstrated that CoAl-LDH was successfully anchored onto BiOBr, as well as formed an intimate interaction. Moreover, the photocatalytic degradation performance of the catalysts/PMS/vis system had been explored under several conditions (e.g., different catalyst doses, PMS doses, anions and pollutants). The 8 wt% CoAl-LDH/BiOBr composite exhibited the highest degradation efficiency (96%) of ciprofloxacin (CIP). In addition, radicals quenching experiments and electron paramagnetic resonance (EPR) indicated that •O2ˉ and 1O2 were the primary radicals for CIP degradation. The photoelectrochemical measurement and photoluminescence (PL) confirmed that 8 wt% CoAl-LDH/BiOBr exhibited the highest separation and transfer rate of charge carriers. The liquid chromatography-mass spectrometer (LC-MS) analysis revealed that oxidation of the piperazine ring and defluorination were the main CIP degradation pathways. Density functional theory (DFT) calculation, including the laplacian bond order (LBO) and Fukui index, which was consistent with the results of LC-MS. This study explained the superiority of the synergistic effect between photocatalysis and PMS activation on the degradation of pollutants.

Construction of direct Z-scheme Bi5O7I/UiO-66-NH2 heterojunction photocatalysts for enhanced degradation of ciprofloxacin: Mechanism insight, pathway analysis and toxicity evaluation

Direct Z-scheme Bi5O7I/UiO-66-NH2 (denoted as BU-x) heterojunction photocatalysts were successfully constructed through ball-milling method. Photocatalytic activities of the as-prepared BU-x samples were determined by using a typical fluoroquinolone antibiotic, ciprofloxacin (CIP). All BU-x heterojunctions exhibited better CIP removal performances than that of pristine Bi5O7I and UiO-66-NH2 upon exposure to white light irradiation. In comparison, the heterojunction with UiO-66-NH2 content of 50 wt% (BU-5) showed excellent structural stability and the optimal adsorption-photodegradation efficiency for the CIP removal. The removal efficiency of CIP (10 mg/L) over BU-5 (0.75 g/L) achieved 96.1% within 120 min illumination. Meanwhile, the effect of photocatalyst dosage, pH and inorganic anions were systemically explored. Reactive species trapping experiments, electron spin resonance (ESR) signals, Mott-Schottky measurements and density functional theory (DFT) simulation revealed that the photo-generated holes (h+), hydroxyl radical (·OH) and superoxide radical (·O2–) played crucial roles in CIP degradation. This result can be ascribed to that the unique Z-scheme charge transfer configuration retained the excellent redox capacities of Bi5O7I and UiO-66-NH2. Meanwhile, the CIP degradation pathways and the toxicity of various intermediates were subsequently analyzed. This work provided a feasible idea for removing antibiotics by bismuth-rich bismuth oxyhalide/MOF-based heterostructured photocatalysts.