Search

Tetracycline (TC), an antibiotic, is persistent in nature and frequently detected in water and sediments. Visible-light-driven photocatalyst for TC degradation is a promising environmental-friendly technology. Bi 2 Zr 2 O 7 , an effective photocatalyst, but no studies on its photodegradation of TC could be found in literature. In this study, Bi 2 Zr 2 O 7 was synthesized by three soft templated sol-gel methods. Three synthesized Bi 2 Zr 2 O 7 catalysts have different structures, morphologies and band gaps. The Bi 2 Zr 2 O 7 nanoparticles synthesized with citric acid as the template (BZO-3) had a larger specific surface area (30.7 m 2 /g) and a narrower band gap (2.39 eV), and exhibited a better performance for TC degradation under visible light with an efficiency of up to 81.3%. They also exhibited good stability and reusability in recycled experiments. A reaction mechanism of TC degradation by these photocatalyst was proposed. The enhanced photocatalytic performance was mainly due to photogenerated holes of reactive species and TC was mainly degraded on the surface of the photocatalyst. Pathways of TC photodegradation were derived from the result of analyses of the reaction intermediates. In conclusion, Bi 2 Zr 2 O 7 nanoparticles were found effective as photocatalyst for TC photodegradation by visible light., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Effect of manganese dioxide (MnO 2 ) on tetracycline (TC) removal/degradation in zero-valent iron (ZVI) based permeable reactive barrier (PRB) system was investigated. To analyze the role of MnO 2 , three different PRB columns packed with ZVI, ZVI and a layer of MnO 2 , and MnO 2 were set up to investigate the removal effect and reaction mechanism of ZVI coupling with MnO 2 on TC removal, respectively. The results show that the removal efficiencies of three PRB columns are 65%, 85%, and 50%, respectively. MnO 2 could accelerate the transformation of Fe 2+ into Fe 3+ and combine with Fe 3+ to degrade TC in different reaction sites in the ZVI-MnO 2 PRB system. Hydroxyl radicals (·OH) were produced in this process, which contributed to about 58.3% for the TC degradation. The UV-Vis spectrum demonstrated that A ring of TC was the main reaction site for interaction with Fe 3+ and the BCD rings were crucial for interactions with MnO 2 . On the basis of intermediates identified by LC-ESI-MS, the ring structure of TC was opened, and low-molecular-weight compounds were produced in ZVI-MnO 2 PRB system., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Ferric nitrate was employed to modify activated carbon prepared from Iris tectorum during H₃PO₄ activation and ability of prepared activated carbon for removal of tetracycline (TC) was investigated. The properties of the activated carbon samples with or without ferric nitrate, ITAC-Fe and ITAC, were measured by scanning electron microscopy (SEM), N₂ adsorption/desorption isotherms, Fourier transform infrared spectroscopy (FTIR) and Boehm's titration. The results showed that mixing with iron increased the BET surface area, total pore volume and the adsorption capacity as compared to the original carbon. FTIR and Boehm's titration suggested that ITAC-Fe was characteristic of more acidic functional groups than ITAC. Adsorption of TC on both samples exhibited a strong pH-dependent behavior and adsorption capacity reduced rapidly with the increasing solution pH. The adsorption kinetics agreed well with the pseudo-second-order model and the adsorption isotherms data were well described by Langmuir model with the maximum adsorption capacity of 625.022 mg/g for ITAC and 769.231 mg/g for ITAC-Fe. The present work suggested that ITAC-Fe could be used to remove tetracycline effectively from aqueous solutions., (© 2013 Elsevier Inc. All rights reserved.)

• The cavitation effect of ultrasound has a reactivation effect on the surface of PRB filler, which solves clogging and sloughing of PRB. • Ultrasound promotes the production of ·OH, an important oxidant in the degradation of tetracycline. • Iron shavings have lower cost, higher degradation efficiency and degradation durability compared to ZVI powders. • The coupling of ultrasound with iron shavings significantly promoted the degradation of cyclic structure tetracycline. Permeable reaction barriers (PRB) with metal particles as the main filler are susceptible to passivation and sloughing, and have a low removal efficiency for organic pollutants. This study proposes a synergistic approach that uses the cavitation effect of ultrasound and the oxidized substances produced in the process to maintain the activity of the PRB packing and improve the removal efficiency. We established and compared three different PRB systems: iron shavings/ZVI powder-only PRB system, ultrasound-only PRB system, and iron shavings/ZVI powder-based ultrasound-PRB system. We highlight differences between systems and quantify the impact of ultrasound. The results showed that the removal of tetracycline (TC) was 66 %/41 %, 20 % and 90 %/60 % for the three PRB systems, respectively. The cavitation effect of ultrasound caused the TC degradation intermediates attached to the surface of iron filler to be stripped into the solution, thus involving the deeper iron in the degradation process and improving the degradation efficiency. Iron shavings showed lower flocculation as well as higher coupling efficiency compared to ZVI powder. The presence of ultrasound increased the ·OH in the Fe-based PRB system by 136 % in 5 min. This study provides a new method for increasing the efficiency of the PRB system in TC degradation. [ABSTRACT FROM AUTHOR]

Tetracycline (TC) infiltrated in groundwater has caused potential threats to the safety of drinking water due to its persistence and high toxicity. In this study, three permeable reactive barrier (PRB) columns packed with zero-valent iron( Fe ), zero-valent iron and microorganism( M + Fe ), microorganism( M ) were employed to investigate the removal effect and reaction mechanism of zero-valent iron coupling with microorganisms on TC removal respectively. The results show that the removal efficiencies of three PRB are about 50%, 40% and 10% respectively. Especially, the effect of coupling ZVI and microbe on the degradation of TC is not a simple superposition. ZVI partially or fully degraded TC by adsorption and reduction. ZVI was converted into Fe 2+ and Fe 3+ while TC was degraded. With the presence of Fe 2+ and Fe 3+ , EPS increased obviously and microbial community structure changed distinctly. It is very interesting that Comamonadaceae , Oxalobacteraceae and Chromatiaceae increased obviously in contrast to no ferric situation, and microbic removal efficiency of TC increased at the same time. [ABSTRACT FROM AUTHOR]

In this research, activated carbon fiber heated by microwave (WACF) under nitrogen (N2) atmosphere adsorption of tetracycline antibiotics (TCs) was analyzed. WACF was obtained under the microwave radiation temperature of 600°C and the radiation time of 15 min. The properties of WACF were characterized by a scanning electron microscope (SEM), N2adsorption/desorption isotherms, and X-ray diffraction (XRD) compared with activated carbon fibers (ACF) without any treatment. WACF had lower surface area (1008 m2/g) but higher external surface area (429 m2/g) than ACF (surface area: 1153 m2/g; external surface area: 308 m2/g). Meanwhile, the adsorption efficiencies of TCs (including tetracycline hydrochloride (TC) and oxytetracycline hydrochloride (OTC)) on WACF were both increased by about 4 times. These results indicated that mesoporosity amplification of WACF played a crucial role in the adsorption capacity of the two TCs. The kinetics and equilibrium data were agreed well with the pseudo-second-order kinetics model (R2 > 0.99) and Langmuir isotherm model (R2 > 0.98), respectively. It suggested that the adsorption process was dominated by chemisorption. Batch experiments showed the maximum adsorption capacities for both adsorbates were 339 and 331 mg/g respectively at pH 2. [ABSTRACT FROM AUTHOR]

Metal-free catalysts are widely considered as promising alternatives to traditional metal-based catalysts, which can effectively activate peroxymonosulfate (PMS). In this study, a novel metal-free catalyst, carbonized polypyrrole (CPPy) was synthesized through high-temperature carbonization of PPy, easily achieving the in situ N doping without the addition of nitrogen sources. Tetracycline (TC) was selected as the target contaminant to assess the catalytic activity of the CPPy/PMS system. Enhanced catalytic activity was observed in CPPy/PMS over a wide pH range (3.0–9.0), and the removal rate of TC by CPPy-3/PMS reached 91.3% after 10 min. After regenerating the used catalyst, the catalytic activity was refreshed, implying its stability and recyclability. The catalytic degradation of TC by CPPy/PMS was mainly attributed to a non-radical process. CPPy, as an intermediary, grabbed electrons from the electron-donating groups of TC and transferred them to the PMS molecule. Thereafter, TC that lost electrons was oxidized and degraded, and the O–O bonds of PMS were destroyed by the transferred electrons to form S O 4 2 − and OH−. Moreover, O ⋅ 2 − and 1O 2 were involved in TC degradation. TC degradation pathway was investigated through HPLC-MS analysis. These findings provide a promising strategy for the construction of catalysts for PMS and environmental remediation. Image 1 • Metal-free N-doped material CPPy was prepared without the addition of N sources. • CPPy/peroxymonosulfate showed excellent catalytic degradation of tetracycline. • The in-situ generation of graphitic N is the key of peroxymonosulfate activation. • The tetracycline degradation is mainly attributed to a non-radical process. [ABSTRACT FROM AUTHOR]

At present, the high re-combination rate of photogenerated carriers and the low redox capability of the photocatalyst are two factors that severely limit the improvement of photocatalytic performance. Herein, a dual Z-scheme photocatalyst bismuthzirconate/graphitic carbon nitride/silver phosphate (Bi 2 Zr 2 O 7 /g-C 3 N 4 /Ag 3 PO 4 (BCA)) was synthesized using a co-precipitation method, and a dual Z-scheme heterojunction photocatalytic system was established to decrease the high re-combination rate of photogenerated carriers and consequently improve the photocatalytic performance. The re-combination of electron-hole pairs (e− and h+) in the valence band (VB) of g-C 3 N 4 increases the redox potential of e− and h+, leading to significant improvements in the redox capability of the photocatalyst and the efficiency of e−-h+ separation. As a photosensitizer, Ag 3 PO 4 can enhance the visible light absorption capacity of the photocatalyst. The prepared photocatalyst showed strong stability, which was attributed to the efficient suppression of photo-corrosion of Ag 3 PO 4 by transferring the e− to the VB of g-C 3 N 4. Tetracycline was degraded efficiently by BCA-10% (the BCA with 10 wt.% of AgPO 4) under visible light, and the degradation efficiency was up to 86.2%. This study experimentally suggested that the BCA photocatalyst has broad application prospects in removing antibiotic pollution. [Display omitted] [ABSTRACT FROM AUTHOR]

• Both synthesis of La 2 Zr 2 O 7 and reduction of GO were accomplished simultaneously in the one-step sol-gel synthetic process. • The maximum TC removal rate and reaction rate constant of LZO/rGO are 82.1% and 0.3097 min−1 at 40 min in visible light. • LZO/rGO exhibited a superior adsorption/photocatalysis synergy. • rGO as electron traps captures photogenerated electrons to inhibit the recombination of electron-hole pairs. In this study, La 2 Zr 2 O 7 /rGO (LZO/rGO) composite photocatalyst was prepared by a one-step sol-gel method, which achieved synthesis of LZO and reduction of GO simultaneously. LZO/rGO-3 (dosage of GO: 0.5 g) was well-crystallized and had the specific surface area of 16.5 m2/g which was higher than that of LZO (9.4 m2/g). Moreover, the introduction of rGO improved the surface microstructure and slightly reduced the band gap (LZO/rGO-3: 2.42 eV), expanding the light absorption range. Tetracycline (TC) was chosen as the target contaminant to assess photocatalytic activity in visible-light. The removal rate and constant of reaction rate (k app) of LZO/rGO-3 was 82.1% and 0.3097 min−1 after 40 min, which was significant higher than that of LZO (57.8% and 0.1741 min−1). In addition, the TC degradation follows pseudo-first-order kinetic and shows the stability after five cycling experiments. The enhanced photocatalytic activity was mainly due to two aspects. Firstly, the improved surface appearance provided more adsorption and reaction sites. Secondly, the rGO as co-catalyst (electron trap) reduced the recombination of electron-hole pairs, and further promoted production of active substances. The photocatalytic mechanism was proposed coupled with analysis of energy structure, active substances and degradation pathways, indicating that h+, 1O 2 , O 2 − and H 2 O 2 were the main active substances in TC photocatalytic degradation, and the generation of 1O 2 was of vital importance. [ABSTRACT FROM AUTHOR]

[Display omitted] • PDS generation in situ by Blue-TNA was used to TC degradation in groundwater. • Coexisting anions inhibit the generation of PDS. • The hydroxyl radical is an important precursor of PDS generation. • TC is degraded through the combined action of PDS, ⋅OH and SO 4⋅−. In this study, a blue titania nanotube array (Blue-TNA) electrode was prepared and applied in oxidizing sulfate ions (SO 4 2−) in groundwater to peroxydisulfate (PDS) for antibiotics degradation. Influencing factors, the mechanism of PDS formation and the efficiency of antibiotics degradation were studied. There was no PDS generation in both the PbO 2 and Pt electrolysis systems over the experimental time, but 2.8 mmol/L PDS was generated in the Blue-TNA electrolysis system in 90 min, which can be attributed to a higher oxygen evolution potential of Blue-TNA than that of PbO 2 and Pt. An increase in current density and Na 2 SO 4 concentration favored PDS generation and the current efficiency improvement. The coexisting anions (CO 3 2−, HCO 3 − and PO 4 3−) inhibited the PDS generation with the strength of inhibition following the sequence: CO 3 2− > HCO 3 − > PO 4 3−. The effect of dissolved oxygen on PDS generation was negligible, but OH was an important precursor for PDS generation based on radical quenching experiments. The degradation efficiency of tetracycline (TC, 20 mg/L) by Blue-TNA was more than 90 % in 30 min due to the synergy of OH and SO 4 − in the sulfate electrolysis system. This study proposed a novel and economic method for PDS generation by the oxidation of SO 4 2− in situ using Blue-TNA, which is an eco-friendly and efficient method in TC degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] • MnO 2 /C@CNT for PMS activation was fabricated via a facile one-pot method. • Increased Mn (III)/Mn (IV) and surface –OH are the basis for high catalytic activity. • SO 4 · - and · OH play dominant roles in TC degradation in the MnO 2 /C@CNT-PMS system. • The toxicity of solution finally decreased after the MnO 2 /C@CNT-PMS process. In this study, a new type of MnO 2 /carbon@carbon nanotubes (MnO 2 /C@CNT) shell-core nanohybrid for peroxymonosulfate (PMS) activation was synthesized by a one-pot method, which simultaneously achieved the synthesis of MnO 2 and assembly of components. Tetracycline (TC) degradation by MnO 2 /C@CNT-PMS was enhanced obviously, and MnO 2 /C@CNT (1.75:1)-PMS systems exhibited the best TC degradation efficiency (85.6%) at 10 min. In addition, the effects of catalyst dosage, PMS dosage, initial pH, reaction temperature, and co-existing ions on the degradation of TC were investigated. The stripping and insertion of the nanocarbon during the synthetic process were the basis for the enhancement of the Mn (III)/Mn (IV) ratio and surface –OH groups, which further accelerated electron transfer and the conversion of Mn and O species. EPR analysis along with the free-radical quenching experiments confirmed the presence of SO 4 · - and · OH during the catalytic reaction, among which SO 4 · - was the main active specie. Moreover, a comprehensive toxicity assay and prediction were performed based on bioluminescence inhibition experiments and the Ecological Structure Activity Relationships (ECOSAR) program. Finally, reasonable degradation pathways of TC were proposed based on LC-MS analysis. [ABSTRACT FROM AUTHOR]