Removal Of Oxytetracycline Research Articles

Antibiotics oxytetracycline removal by photocatalyst titanium dioxide and graphitic carbon nitride in aquaculture wastewater

The surge in the use of antibiotics, especially in aquaculture, has led to development of antibiotic resistance genes, which will harm environmental and public health. One of the most commonly used antibiotics in aquaculture is oxytetracycline (OTC). Employing photocatalysis, this study compared OTC degradation efficiency of two different types of common photocatalysts, TiO2 and graphitic carbon nitride (GCN) in terms of their photochemical properties and underlying photocatalytic mechanism. For reference purpose, self-synthesized GCN from urea precursor (GCN-Urea) and commercial GCN (GCN-Commercial) were both examined. OTC adsorption-photocatalysis removal rates in pure OTC solution by TiO2, GCN-Urea and GCN-Commercial were attained at 95%, 60% and 40% respectively. Photochemical properties evaluated included light absorption, band gap, valence and conduction band positions, photoluminescence, cyclic voltammetry, BET surface area and adsorption capability of the photocatalysts. Through the evaluations, this study provides novel insights towards current state-of-the-art heterogeneous photocatalytic processes. The electron-hole recombination examined by photoluminescence is not the key factor influencing the photocatalytic efficacies as commonly discussed. On the contrary, the dominating factors governing the higher OTC degradation efficiency of TiO2 compared to GCN are the high mobility of electrons that leads to high redox capability and the high pollutant-photocatalyst affinity. These claims are proven by 86% and 40% more intense anodic and cathodic cyclic voltammetry curve peaks of TiO2 as compared to both GCNs. OTC also demonstrated 1.7 and 2.3 times higher affinity towards TiO2 than GCN-Urea and GCN-Commercial. OTC removal by TiO2 in real aquaculture wastewater only achieved 50%, due to significant inhibition effect by dissolved solids, dissolved organic matters and high ionic contents in the wastewater.

Magnetic CuFe2O4 nanoparticles anchored on N-doped carbon for activated peroxymonosulfate removal of oxytetracycline from water: Radical and non-radical pathways

In this work, magnetic CuFe2O4 was prepared for the removal of oxytetracycline (OTC) by a self-propagating combustion synthesis method. Almost complete degradation (99.65%) of OTC was achieved within 25 min at [OTC]0 = 10 mg/L, [PMS]0 = 0.05 mM, CuFe2O4 = 0.1 g/L under pH = 6.8 at 25 °C for deionized water. Specially, the addition CO32− and HCO3− induced the CO3•- appearance enhancing the selective degradation to electron-rich OTC molecule. The prepared CuFe2O4 catalyst exhibited desirable OTC removal rate (87.91%) even in hospital wastewater. The reactive substances were analyzed by free radical quenching experiments and electron paramagnetic resonance (EPR), and the results demonstrated that 1O2 and •OH were the main active substances. Liquid chromatography-mass spectrometry (LC-MS) was used to analyze the intermediates produced during the degradation of OTC and thus to speculate on the possible degradation pathways. Ecotoxicological studies were conducted to unveil large-scale application prospect.

S-scheme heterojunction between MOFs and Ag3PO4 leads to efficient photodegradation of antibiotics in swine wastewater

Antibiotics in swine wastewater could lead to risks to the environment and human health, and it is a competitive alternative to degrade antibiotics via photocatalysis which is green and eco-friendly. However, charge separation efficiency and light absorption capacity have been key factors limiting the technology. In this work, we synthesized the novel photocatalysts of MOF-545/Ag3PO4 via solvothermal methods, and examine the performance and mechanism for the degradation of oxytetracycline (OTC) in swine wastewater. The results showed that compared with Ag3PO4, the composite catalysts have stronger photoresponse and charge separation ability. MOF-545/Ag3PO4 could completely degrade OTC within 3.0 min with a rate constant of 3.97 min−1 which is 12.9 times that of Ag3PO4. OTC removal was still 100% within 3.0 min after 5 cycles, which confirmed that the composite catalyst was stable. Data from free radical capture tests showed that photogenerated holes (h+) and superoxide radicals (•O2–) played a dominant role in OTC degradation. In-situ X-ray photoelectron spectroscopy (XPS) spectra and electron spin resonance (ESR) spectra proved the formation of an S-scheme heterojunction in MOF-545/Ag3PO4, which greatly improves the carrier separation efficiency of catalysts. This study provides a novel MOF-based catalyst for improving photocatalytic performance.

Boosting electron transfer in Cu2O@PDA hollow fiber membranes to decompose oxytetracycline under visible light with persulfate

In this study, a polydopamine (PDA)-functional hollow fiber membrane (HFM) modified by Cu2O (Cu2O/PDAHFM) was developed via photocatalysis coupled persulfate activation for oxytetracycline (OTC) degradation. It is found that PDA facilitates electron transfer and therefore promotes OTC degradation, achieving 96% removal efficiency. The quenching experiments and electron paramagnetic resonance (EPR) experiments demonstrated that •SO4−, •OH, •O2−, 1O2, and h+ contributed to the OTC removal. Based on intermediates identified by liquid chromatograph mass spectrometer (LC-MS), three possible degradation pathways of OTC were proposed. The toxicity of intermediates was evaluated by using Toxicity Estimation Software Tool (T.E.S.T.). Moreover, the Cu2O/PDAHFM can achieve more than 80% removal of OTC after 6 cycles, demonstrating the reusability of the catalyst. In addition, flow reactors with two types of membrane modules for continuous wastewater were constructed, and computational fluid dynamics (CFD) was used to simulate the mass transfer and degradation processes to compare the two reactors for degrading contaminants. This work provides deep insight into the mechanisms of photocatalysis coupled with persulfate activation for OTC degradation and an alternative method for designing wastewater treatment devices.

Comparison of Ten Metal-Doped LaFeO3 Samples on Photocatalytic Degradation of Antibiotics in Water under Visible Light: Role of Surface Area and Aqueous Phosphate Ions.

Doping semiconducting oxides, such as LaFeO3 (LF), with metallic elements is a good strategy to improve the performance of photocatalysts. In this study, LF and ten different nanopowders metal-doped at the La or Fe site of LaFeO3 were evaluated in the photocatalytic degradation of ciprofloxacin (CP) and oxytetracycline (OTC). The following metals were used in the doping (mol%) process of LF: Pd 3% and 5%; Cu 10%; Mg 5%, 10%, and 20%; Ga 10%; Y 10% and 20%; and Sr 20%. The doped samples were synthetized using a citrate auto-combustion technique. From the X-ray diffraction (XRD) data, only a single crystalline phase, namely an orthorhombic perovskite structure, was observed except for trace amounts of PdO in the sample with Pd 5%. The specific surface area (SSA) ranged from 9 m2 g-1 (Ga 10%) to 20 m2 g-1 (Mg 20%). SEM images show that all samples were constituted from agglomerates of particles whose sizes ranged from ca. 20 nm (Mg 20%) to ca. 100 nm (Pd 5%). Dilute aqueous solutions (5 × 10-6 M) prepared for both CP and OTC were irradiated for 240 min under visible-light and in the presence of H2O2 (10-2 M). The results indicate a 78% removal of OTC with Cu 10% doped LF in a phosphate buffer (pH = 5.0). The degradation of CP is affected by pH and phosphate ions, with 78% (in unbuffered solution) and 54% (in phosphate buffer, pH = 5.0) removal achieved with Mg 10% doped LF. The reactions follow a pseudo-first order kinetic. Overall, this study is expected to deepen the assessment of photocatalytic activity by using substrates with different absorption capacities on photocatalysts.

Multiphasic MoS2 activates peroxymonosulfate for efficient removal of oxytetracycline: The dominant role of surface reactive species

The utilization of Fenton-like reactions to generate reactive species is a potential solution to the escalating environmental pollution. In this study, a series of MoS2 samples with different 1T/2H phase ratios and S vacancies are fabricated, and approximately 100% oxytetracycline (OTC) is removed in 1-MoS2/peroxymonosulfate (PMS) system within 60 min. The results show that the 1T/2H phase ratio, instead of S vacancy, dominates the catalytic performance, additionally, the rate constants (kobs) value (0.11 min−1) of MoS2 with approximately 49.3% 1T phase (1-MoS2) is 3.67 times that (0.03 min−1) of MoS2 with 2.0% 1T phase (3-MoS2). Various reactive species including SO4•−, •OH, O2•–, and 1O2 are generated in the MoS2/PMS system, however, the activation of PMS by multiphasic MoS2 cannot be determined based on the amount if aqueous reactive species. Combining the results of electron paramagnetic resonance, quenching experiments and density functional theory calculations, we confirmed that 1-MoS2 can activate PMS and generate more active species than 3-MoS2, however, more active species are bound on the surface of 1-MoS2. In addition, the excellent electron transfer capability of 1-MoS2 contribute to the activation of PMS, and 1-MoS2 exhibits excellent catalytic performance after three cycles. The toxicity of OTC reduced after reaction in the 1-MoS2/PMS system. This study provides novel insights into the internal mechanism of multiphasic phase MoS2/PMS systems.

Cometabolic biotransformation mediates the detoxification of oxytetracycline in Flavobacterium-enriched microbiome

Oxytetracycline (OTC), a widely used antibiotic that is readily detectable in the environment, potentially has a number of negative ecological consequences. The present study revealed the key role of the cometabolic breakdown of OTC in activated sludge microbiomes, which led to a high removal efficiency and detoxification of both OTC and its derivatives. An AS bioreactor was established to treat environmentally relevant levels of OTC. The bioreactor achieved an overall OTC removal efficiency of 94–97% at the steady state, with cometabolic biotransformation as the primary contributor to this ahead of other removal routes such as direct metabolic biodegradation, biosorption, and phosphorolysis. A novel biotransformation pathway for OTC proposed in this study involved dehydration, hydroxylation, ring cleavage, and alcohol dehydrogenation, distinguishing it from previously reported pathways. Although transformation products with potentially higher toxicity than OTC formed during the biotransformation process, the AS microbiome eliminated the overall toxicity of both OTC and its derivatives, as illustrated by both molecular structure-based toxicity simulations and antimicrobial susceptibility testing. Analysis of microbiome sequence data revealed the bacterial populations potentially facilitating cometabolic (e.g., Tolumonas) and direct metabolic (e.g., Flavobacterium) biotransformation. Overall, our study provides new insights into the removal routes and kinetics for OTC in AS microbiomes and the key species that potentially promote OTC transformation and detoxification.

Dual-functional fluorescent metal-organic framework based beads for visual detection and removal of oxytetracycline in real aqueous solution

The development of metal-organic frameworks (MOFs) based materials with specific structures and functions has important significance and application value in energy, environment, and material science. Herein, we developed a novel zinc-based MOF with 2-(4-carboxyphenyl)-1H-benzo[d]imidazole-5-carboxylic acid (CBC) as ligand, Zn-CBC, which exhibited large surface area, porous structure, and blue fluorescence. The material was demonstrated for simultaneous visual detection and removal of oxytetracycline (OTC) as a dual-functional platform. With the introducing of OTC that can be adsorbed by the surface group of Zn-CBC, the fluorescence emission intensity centered at 472 nm was significantly decreased attributed to the internal filtering effect (IFE) between OTC and Zn-CBC. In addition, due to the aggregation-induced emission (AIE) of OTC in the porous structure of Zn-CBC, a new fluorescence emission maximum at 540 nm appeared, which constructed a blue to yellow-green ratiometric fluorescence system. Combing the optical and adsorption properties of Zn-CBC, we innovatively prepared Zn-CBC MOF-alginate-Ca2+-polyacrylic acid polymer beads (MACPs) for sensing and removing of OTC in real water samples, which showed wide applicability in practical applications.

Facile synthesis of reusable Ag/TiO2 composites for efficient removal of antibiotic oxytetracycline under UV and solar light irradiation

BackgroundsIn this work, Ag-doped TiO2 nanomaterials (TiAgx, where x denotes the weight percentage of Ag) were prepared using a facile one-step sol-gel technique. The combination of Ag with TiO2 promises to enhance the lifetime of photogenerated electron-hole pairs and widen the photocatalytic activity in the visible light region, leading to improved photocatalytic activity. MethodsThe synthesized materials were characterized using different analyses and afterwards applied as photocatalysts to degrade oxytetracycline (OTC) in aqueous solution under ultraviolet (UV) and solar light illumination. Significant findingsThe highest photocatalysis was achieved for TiAg2 with 99.6% OTC removal after 120-min UV irradiation. Moreover, the best OTC removal under solar light irradiation was gotten for TiAg5, of which 94.1% of OTC was removed after 180 min. Reactive species of ∙O2− radicals were presented as the dominant agents in OTC oxidization; meanwhile, ∙OH and h+ contributed to the photodegradation process. The mineralization efficiency of OTC using TiAg2 reached 59.6% after 240-min UV irradiation. Furthermore, the OTC removal of TiAg2 by photocatalysis still maintained over 97% after 5 cycles.

Rape Straw Supported FeS Nanoparticles with Encapsulated Structure as Peroxymonosulfate and Hydrogen Peroxide Activators for Enhanced Oxytetracycline Degradation

Iron-based catalysts with high load content of iron sulfide (FeS) were commonly peroxymonosulfate (PMS) and hydrogen peroxide (H2O2) activators to degrade organic pollutants but limited catalytic efficiency and increased risk of ferrous ion leaching restricted their use. Meanwhile, various biomass materials such as straw, peel, and branch have been extensively prepared into biochar for mechanical support for iron-based catalysts; however, the preparation process of biochar was energy-intensive. In this study, FeS nanoparticles modified rape straw composites (RS-FeS) encapsulated with ethylenediaminetetraacetic acid (RS-EDTA-FeS) were successfully presented by in-situ synthesis method for efficiently activating PMS and H2O2 to degrade oxytetracycline (OTC), which was economical and environmentally friendly. The results showed that the modified rape straw can remove OTC efficiently, and the addition of EDTA also significantly enhanced the stability and the reusability of the catalyst. In addition, EDTA also promoted the activation of H2O2 at neutral pH. The OTC degradation efficiency of the two catalysts by PMS was faster than that of H2O2, but H2O2 had a stronger ability to remove OTC than PMS. The highest OTC removal efficiency of RS-FeS and RS-EDTA-FeS were 87.51 and 81.15%. O2•- and 1O2 were the major reactive oxidative species (ROS) in the PMS system. Furthermore, compared with RS-FeS, the addition of EDTA inhabited the generation of O2•- in the PMS system. Instead, O2•- and •OH were the major ROS in the H2O2 system, but 1O2 was also identified in RS-FeS/H2O2 system. RS-EDTA-FeS showed a trend of rising first and then decreasing in recycle test. Instead, the removal rate of OTC by RS-FeS decreased significantly with the increase in reuse times. In the actual wastewater test, the TOC removal of two catalysts active by H2O2 was better than PMS, which was consistent with the test results of OTC, indicating that the two catalysts have application value in the removal of organic pollutants in actual wastewater. This study directly used plant materials as catalysts and omits the preparation process of biochar, greatly reduces the preparation cost and secondary pollution of catalysts, and provides theoretical support for the deepening of advanced oxidation technology.

Synergy between graphitized biochar and goethite driving efficient H2O2 activation: Enhanced performance and mechanism analysis

Due to the contradiction between attractive properties and undesirable Fenton-like catalytic performance of iron minerals, how to enhance their Fenton-like catalytic activity is a critical but challenging issue. Here, we took an eco-friendly approach to improve the Fenton-like catalytic capacity of goethite (α-FeOOH) by loading it on graphitized biochar (GBC), and the results indicated that the existence of GBC could successfully facilitate the oxytetracycline (OTC) removal. The degradation rate constant of α-FeOOH/GBC-10 composite was approximately 2.1 times higher than that of α-FeOOH. GBCs with different graphitization degrees were obtained by adjusting the pyrolysis temperature. Interestingly, the improvement of catalytic activity of α-FeOOH/GBC was well correlated with the graphitization degree of GBC, and the graphitized structures (sp2-C) and functional group (CO) in GBC could expedite the blocked Fe(III)/Fe(II) cycling by speeding up the electrons transfer from H2O2 to α-FeOOH and donating electrons to Fe(III). In addition, the electron spin resonance and quenching experiments demonstrated that OTC removal was attributed to the joint action of •OH, O2−, and 1O2. This study sheds light on the possible role of GBC in Fenton-like reactions based on iron minerals and thus, lays the groundwork for the rational construction of more efficient Fenton-like catalytic systems.

Insight into boron-doped biochar as efficient metal-free catalyst for peroxymonosulfate activation: Important role of -O-B-O- moieties.

In recent years, metal-free catalysts for persulfate-mediated oxidation processes have been widely applied to remove contaminants in the aquatic environment. Herein, a simple pyrolysis approach was used to synthesize the boron doped biochars (B@TBCs) derived from boric acid mixed with tea seed shells powders. The obtained B@TBCs exhibited fantastic capability to boost PMS (0.5mM) activation for 90%∼ removal of oxytetracycline (OTC) within 20min. Through the correlation analysis and DFT calculations, it was concluded that the apparent rate constant of pollutants removal was greatly related to the -O-B-O- groups on the biochars, which could improve the electron-donating capacity of the biochar. In addition, the degradation process of OTC was pH-dependent because of the changed roles of ROSs under different pH. Finally, according to the DFT calculation, LC-MS and toxicological analysis, the degradation pathways of pollutants and the toxicity changes during the degradation process were obtained. These findings consolidated the theoretical basis for further boosting the catalytic activity of B-doped biochars and expanded the imagination for the modification of other metal-free biochar catalysts for PMS activation.

Degradation of Oxytetracycline and Chlortetracycline by Fenton Process

In this study, degradation of oxytetracycline (OTC) and chlortetracycline (CTC) was investigated by Fenton process. In experimental studies conducted for this purpose, different values of pH, Fe2+ concentration, H2O2 concentration and reaction time were tested as important parameters for the Fenton process and optimum conditions for OTC and CTC removal were determined. For both antibiotics, the optimum values of the parameters in the Fenton process were the same, and these values were found to be 3 for pH, 20 mg/L for Fe2+ concentration, 25 mg/L for H2O2 concentration, 5 min for reaction time. Under these optimum conditions, OTC degradation was 100%, CTC degradation was 99.68%, chemical oxygen demand (COD) removal efficiency for oxytetracycline (O-COD) was 89.6%, COD removal efficiency for chlortetracycline (C-COD) was 88.5%. These results show that the Fenton process is an effective method that can be used for OTC and CTC degradation.

Simultaneous degradation of antibiotic and removal of phosphate in water by a O3/CaO2 advanced oxidation process

The simultaneous presence of antibiotics and phosphate (P) in wastewater will threaten human health and ecological security. The purpose of this study is to study the simultaneous removal of oxytetracycline (OTC) and P in water by O3/CaO2 advanced oxidation process. With enhancing CaO2 dosage, the degradation efficiency of OTC first improved and then declined, whereas the removal efficiency of P kept increasing. Increasing the amount of O3 increased the removal efficiency of OTC, but had little effect on the removal efficiency of P. With 0.80 g/L CaO2 and 0.50 g/h O3, the removal efficiency of OTC and P reached 98.0 % and 90.5 % respectively. The lower OTC concentration was beneficial to OTC degradation and P precipitation. The P concentration has no effect on OTC degradation, but it would affect itself precipitation. Alkaline environment was conducive to OTC degradation and P removal. ·OH, ·O2−, 1O2 made major contribution to the degradation of OTC, which was verified by ESR technique and free radical capture experiment. During the degradation of OTC and P removal, TOC and COD values decreased, while pH and conductivity showed a downward trend. Based on UV–Vis spectrum, 3D EEMF spectrum and LC-MS analysis, two main degradation pathways of OTC were proposed. Toxicity analysis of intermediates showed that their toxicity was significantly lower than that of OTC. The O3/CaO2 system can be considered as an efficient and prospective method for the simultaneous removal of OTC and P in water.

Adsorptive removal of oxytetracycline in wastewater by Cu/Al doped carbon microspheres prepared from low-molecular-weight chitosan

A series of Cu/Al doped nitrogen-containing carbon microspheres prepared from low-molecular-weight chitosan (Cu/Al@NC-x, x = 1, 2, 3) were synthesized by a facile one-pot hydrothermal strategy and used for the adsorptive removal of oxytetracycline (OTC) contaminants to polish up the quality of water. Batch adsorptive experiments were performed to appraise the potential of Cu/Al@NC-x as an effective adsorbent for OTC. The effects of initial OTC concentration, solution pH, coexisting ions, adsorption time, and temperature on adsorptive performance were systematically studied. Cu/Al@NC-2 possessed the highest adsorption performance for OTC with maximum equilibrium adsorption capacity of 1727.65 mg g−1 (25 °C), 2583.10 mg g−1 (35 °C), and 2900.84 mg g−1 (45 °C), respectively. The kinetics and isotherm simulation data complied well with the pseudo-second-order kinetic and Langmuir isotherm models, respectively. The thermodynamic analysis (ΔH° > 0, ΔG° < 0) illustrated the spontaneous endothermic process of Cu/Al@NC-2 adsorbing OTC. Especially, Cu/Al@NC-2 still retained an excellent removal efficiency of 92.25 % for OTC after five adsorption cycles, verifying the feasibility of Cu/Al@NC-2 in antibiotic wastewater treatment.

Biological detoxification of oxytetracycline using Achromobacter-immobilized bioremediation system

Oxytetracycline (OTC) is widespread in the environment, posing potential ecological health risks. This work aimed to develop a bioremediation system that can biotransform and detoxify continuous OTC-bearing streams. An OTC-removing organism, Achromobacter sp. ONK, was isolated from activated sludge enriched with OTC. ONK removed OTC via co-metabolic biotransformation. A series of batch experiments were performed to determine the biotransformation kinetics (1.5–2.1 d−1) at varying levels of OTC and the optimal operating conditions (i.e., 2.0 g/L biomass and 0.2 g/L glucose as a carbon source) for OTC removal. A bioremediation system for treating continuous OTC streams was developed by immobilizing ONK using a natural alginate polymer. The immobilized-ONK bioremediation system demonstrated a > 60 % removal of OTC with a hydraulic retention time of 10 h and detoxified OTC using two novel transformation pathways that were validated by both structure-based modeling and experimental results. This study has practical implications for the development of an effective bioremediation process for detoxifying pharmaceutical waste streams.

Ultra-thin DyFeO3/g-C3N4 p-n heterojunctions for highly efficient photo-Fenton removal of oxytetracycline and antibacterial activity

The design and synthesis of visible light-responsive heterogeneous catalysts for the effective removal of contaminants are critical areas of research in the environmental catalysis. In this study, DyFeO3/g-C3N4 p-n heterojunctions (DFCs) were successfully synthesized. TEM, HRTEM, SEM, FTIR and XPS results clarified the successful formation of DFCs and their ultra-thin and porous structure. DRS and XPS VB spectra revealed that the DFCs were type Ⅱ heterojunctions with strong visible light absorption. TPC, EIS, PL and PL decay spectra confirmed the increase of the separation efficiency and the inhibition of the recombination of the photogenerated charge carriers in DFCs. DFC-2 (containing 2 wt% of DyFeO3) exhibited the best photo-Fenton degradation performance. The highest degradation efficiency was 99.1%, 100%, and 99.6% on DFC-2 for oxytetracycline, methylene blue, and rhodamine B, respectively. The photo-Fenton antibacterial efficiency was over 99% after 15 min of visible light irradiation. Moreover, the antibacterial effect was 4 times and 2.7 times that of photocatalytic or Fenton antibacterial processes. The internal electric field generated at the interface between DyFeO3 and g-C3N4 ameliorated the spatial separation and transfer features of charge carriers. In addition, the accelerated transfer of the electrons facilitated the reduction of Fe3+ to regenerate Fe2+, which further enhanced the photo-Fenton degradation and antibacterial activity. In a radical scavenger experiment, ESR and HPLC-MS were employed to identify the major active species and intermediates in the photo-Fenton degradation of oxytetracycline. The degradation pathways and mechanism were reasonably inferred. This study proposes promising DFCs with p-n heterostructures for the effective photo-Fenton removal of oxytetracycline and antibacterial activity.

Enhancement on removal of oxytetracycline in aqueous solution by corn stover biochar: Comparison of KOH and KMnO4 modifications

In this study, corn stover biochar (CSBC) and KOH and KMnO4 modified corn stover biochars (HCSBC and MCSBC) were used for oxytetracycline (OTC) removal and the enhancement of the modification was investigated. The modifications of KOH and KMnO4 improved the physical and chemical properties of CSBC (e.g., pore structure, surface morphology, crystal structure, surface functional groups, and distribution and binding state of surface elements), which significantly contributed to the removal of OTC. The removals of OTC by CSBC, HCSBC and MCSBC were multilayer, and their maximum removal amounts were 26.21 mg/g, 48.30 mg/g and 200.4 mg/g, respectively. The removals of OTC by CSBC, HCSBC and MCSBC were a combination of physical and chemical actions, but the chemical action was dominant. The rates of OTC removal by CSBC and HCSBC depended on liquid film diffusion and intraparticle diffusion, while the rate-controlling step of OTC removal by MCSBC was only liquid film diffusion. Meanwhile, the removals of OTC by CSBC, HCSBC and MCSBC were spontaneous and endothermic, and the randomness of the solid-liquid interface was irregularly increased during the process. Furthermore, the mechanisms of OTC removal by CSBC and HCSBC should be the same, and the enhancement of OTC removal by HCSBC may be attributed to the increase of active sites. The increase of active sites and degradation together resulted in that removal capacity of MCSBC was the greatest, and the contribution of degradation should be dominant. Most of the OTCs and their degradation products were attached to HCSBC and MCSBC via hydrogen bonding, π-π interactions and complexation.

Enhanced removal of oxytetracycline from aquatic solution using MnOx@Fe3O4 bimetallic nanoparticle coated powdered activated carbon: synergism of adsorption and chemical autocatalytic oxidation processes

The existence of MnOx@Fe3O4 bimetallic nanoparticles improved the adsorption capacities by increasing the adsorption sites of PAC and the self-catalytic reaction extended the service life of MnOx@Fe3O4-PAC without additional use of oxidants.

Visible Light Activated Fe-N-SiO2/TiO2 Photocatalyst: Providing an Opportunity for Enhanced Photocatalytic Degradation of Antibiotic Oxytetracycline in Aqueous Solution

To probe advantages in Fe-N-SiO2/TiO2 nanocomposite system, the visible photocatalytic degradation of the nonbiodegradable antibiotic oxytetracycline (OTC) by unsupported TiO2 and its modified composites by incorporating each of the Fe, N, and SiO2 dopants under a series of conditions were investigated. The structural and optical properties as well as the morphology of the prepared nanocomposites were also characterized applying Fourier transform infrared (FT-IR), X-ray diffraction, photoluminescence spectroscopy, UV-visible diffuse reflectance spectra and field emission scanning electron microscopy/Energy-dispersive X-ray spectroscopy (FESEM/EDX). In order to develop two models portraying appropriate functional relationships between two main responses (OTC removal efficiency and its specific removal rate (SRR)) and four numerical variables (OTC concentration, catalysis loading, initial pH and reaction time), two separate multivariate analysis pathways under response surface methodology (RSM) were taken. The results obtained all came down to the maximum SRR (220 OTC mg OTC removed/g cat. h) found at the maximum catalyst dosage of 1.5 g/l, and acidic pH of 3 after 0.5 h. Furthermore, the Fe-N-SiO2/TiO2 proved a stable photocatalytic activity during three subsequent reusability experiments, shedding light on its reliable potential for future application.