Effect and mechanism analysis of MnO2 on permeable reactive barrier (PRB) system for the removal of tetracycline

Characteristics of biological manganese oxides produced by manganese-oxidizing bacteria H38 and its removal mechanism of oxytetracycline

Oxytetracycline (OTC) is widely used in clinical medicine and animal husbandry. Residual OTC can affect the normal life activities of microorganisms, animals, and plants and affect human health. Microbial remediation has become a research hotspot in the environmental field. Manganese oxidizing bacteria (MnOB) exist in nature, and the biological manganese oxides (BMO) produced by them have the characteristics of high efficiency, low cost, and environmental friendliness. However, the effect and mechanism of BMO in removing OTC are still unclear. In this study, Bacillus thuringiensis strain H38 of MnOB was obtained, and the conditions for its BMO production were optimized. The optimal conditions were determined as follows: optimal temperature = 35 °C, optimal pH = 7.5, optimal Mn(Ⅱ) initial concentration = 10 mmol/L. The results show that BMO are irregular or massive, mainly containing MnCO3, Mn2O3, and MnO2, with rich functional groups and chemical bonds. They have the characteristics of small particle size and large specific surface area. OTC (2.5 mg/L) was removed when the BMO dosage was 75 μmol/L and the solution pH was 5.0. The removal ratio was close to 100 % after 12 h of culture at 35 °C and 150 r/min. BMO can adsorb and catalyze the oxidation of OTC and can produce ·O2-, ·OH, 1O2, and Mn(Ⅲ) intermediate. Fifteen products and degradation pathways were identified, and the toxicity of most intermediates is reduced compared to OTC. The removal mechanism was preliminarily clarified. The results of this study are convenient for the practical application of BMO in OTC pollution in water and for solving the harm caused by antibiotic pollution.

Selective efficient photocatalytic degradation of antibiotics and direct Z-type migration pathway for hierarchical core-shell TiO2/g-C3N4 composites

Constructing superior Z-type photocatalytic heterojunction is beneficial to effectively enlarge interface contact, improve the photo-generated carrier separation rate, and retain the high redox ability. In this work, we designed a hierarchical core-shell g-C3N4/TiO2 structure to build Z-type heterojunction via combining simple template method and pyrolysis process. A close-knit Z-type heterojunction was constructed using TiO2 as a thick core and g-C3N4 as an ultra-thin shell. The effects of lamp source, wavelength, tetracycline (TC) concentration, and photocatalyst dose on the degradation performance on TC of g-C3N4/TiO2 were inspected. 0.1TiO2/g-C3N4 photocatalyst had the best degradation rate and highest removal rate within 30 min, and its degradation rate was about 49, 23, and 5 times than pure g-C3N4, TiO2, and commercial TiO2/g-C3N4 in respect. Moreover, compared with degradation ability under Xenon lamp, LED irradiation for g-C3N4/TiO2 composites showed a remarkable selective degradation. The fast and efficient Z-type transfer pathway of 0.1 g-C3N4/TiO2 was realized by forming an optimized interface and abundant surface active sites ascribed to the combined action of thick TiO2 core and ultra-thin g-C3N4 shell. In addition, the degradation intermediates were analyzed by LC-MS and suggested pathways of degradation. The work could provide novel design concept to obtain reliable Z-type photocatalysts with hierarchical core-shell structure applied in degradation of antibiotic wastewater.

Investigating the different transformations of tetracycline using birnessite under different reaction conditions and various humic acids

Prior studies have successfully used manganese oxides to facilitate the transformation of tetracycline in aqueous solution. To further understand the kinetic and the transformation pathway of tetracycline via birnessite (δ-MnO2) under different conditions, experiments were conducted at pH levels of 3, 6, and 9 in the presence or absence of Aldrich humic acid (ADHA). Tetracycline removal followed the pseudo-second-order reaction model in all investigated cases, and the removal efficiency (g mg-1 h -1) followed the following trend: pH 3 (0.45/0.27) > pH 6 (0.036/0.087) > pH 9 (0.036/0.103) in the absence/presence of ADHA. Liquid chromatography-mass spectrometry/mass spectrometry results identified five main transformation products at m/z 495, 477, 493, 459, and 415, produced by the transformation reactions, including hydration, oxidation, desaturation, and oxy reduction. Notably, in the presence of ADHA at pH 3, products with higher toxicity secondary (m/z 477 and 495) were reduced, while less toxicity products (m/z 459 and 415) were enhanced. The experiments utilizing tetracycline and δ-MnO2 with varied humic acids (HA) revealed that HA with high polar organic carbon groups, such as O-alkyl, exhibited higher removal efficiency at pH 6. This research offers the first comprehensive insights into the pathway transformations of tetracycline via δ-MnO2 under different pH conditions and HA types. For further understanding, future work should investigate the binding of HA, TTC, and/or Mn2+ and the oxidation capacity of MnO2 after the reaction to clarify Mn2+ elution mechanisms.

Monitoring the remediation of groundwater polluted by MSW landfill leachates by activated carbon and zeolite with spectral induced polarization technique

The municipal solid waste (MSW) landfill in Hangzhou, China utilized zeolite and activated carbon (AC) as permeable reactive barrier (PRB) fill materials to remediate groundwater contaminated with MSW leachates containing ammonium, chemical oxygen demand (COD), and heavy metals. The spectral induced polarization (SIP) technique was chosen for monitoring the PRB because of its sensitivity to pore fluid chemistry and mineral-fluid interface composition. During the experiment, authentic groundwater collected from the landfill site was used to permeate two columns filled with zeolite and AC, and the SIP responses were measured at the inlet and outlet over a frequency range of 0.01-1000 Hz. The results showed that zeolite had a higher adsorption capacity for COD (7.08 mg/g) and ammonium (9.15 mg/g) compared to AC (COD: 2.75 mg/g, ammonium: 1.68 mg/g). Cation exchange was found to be the mechanism of ammonium adsorption for both zeolite and AC, while FTIR results indicated that π-complexation, π-π interaction, and electrostatic attraction were the main mechanisms of COD adsorption. The Cole-Cole model was used to fit the SIP responses and determine the relaxation time (τ) and normalized chargeability (mn). The calculated characteristic diameters of zeolite and AC based on the Schwarz equation and relaxation time (τ) matched the pore sizes observed from SEM and MIP, providing valuable information on contaminant distribution. The mn of zeolite was positively linear with adsorbed ammonium (R2 = 0.9074) and COD (R2 = 0.8877), while the mn of AC was negatively linear with adsorbed ammonium (R2 = 0.8192) and COD (R2 = 0.7916), suggesting that mn could serve as a surrogate for contaminant saturation. The laboratory-based real-time non-invasive SIP results showed good performance in monitoring saturation and provide a strong foundation for future field PRB monitoring.

Enhanced degradation of oxytetracycline in aqueous solution by DBD plasma-coupled vacuum ultraviolet/ultraviolet (VUV/UVC) system

A systematic investigation of coupling dielectric barrier discharge (DBD) plasma and different ultraviolet bands (UVA, UVB, UVC, and VUV) was constructed for antibiotic-contaminant wastewater treatment. Compared with DBD, UV, or other combined DBD/UV systems, the DBD/VUV/UVC system exhibited excellent degradation and mineralization efficiencies for oxytetracycline (OTC), achieving 93.2% removal rate (reaction rate constant 1.05 min^-1) and higher decarbonization efficiency (mineralization rate 0.47 mg C min^-1) within 2.5 min treatment. The radical quenching tests revealed that HO⋅, [Formula: see text] , and ¹O₂ were all involved in the decomposition of OTC in the DBD/VUV/UVC system, among which [Formula: see text] played a dominant role. Possible degradation pathways of OTC in the DBD/VUV/UVC process were proposed using density functional theory and detected intermediates. Four indexes were used to assess the toxicity of OTC and its degraded intermediates. The inorganic anions and HA slightly reduced the degradation efficiency of the DBD/VUV/UVC system. This research provides new ideas to broaden the application of plasma and alleviate the water environment crisis.

A comprehensive review on permeable reactive barrier for the remediation of groundwater contamination

Groundwater quality is deteriorating due to contamination from both natural and anthropogenic sources. Traditional "Pump and Treat" techniques of treating the groundwater suffer from the disadvantages of a small-scale and energy-intensive approach. Permeable reactive barriers (PRBs), owing to their passive operation, offer a more sustainable strategy for remediation. This promising technique focuses on eliminating heavy metal pollutants and hazardous aromatic compounds by physisorption, chemisorption, precipitation, denitrification, and/or biodegradation. Researchers have utilized ZVI, activated carbon, natural and manufactured zeolites, and other by-products as reactive media barriers. Environmental parameters, i.e., pH, initial pollutant concentration, organic substance, dissolved oxygen, and reactive media by-products, all influence a PRB's performance. Although their long-term impact and performance are uncertain, PRBs are still evolving as viable alternatives to pump-and-treat techniques. The use of PRBs to remove anionic contaminants (e.g., Fluoride, Nitrate, etc.) has received less attention since precipitates can clog the reactive barrier and hinder groundwater flow. In this paper, we present an insight into this approach and the tremendous implications for future scientific study that integrates this strategy using sustainability and explores the viability of PRBs for anionic pollutants.

Comparison of O3, UV/O3, and UV/O3/PS processes for marine oily wastewater treatment: Degradation performance, toxicity evaluation, and flocs analysis

Efficient on-site treatment technology is crucial for mitigating marine oily wastewater pollution. This work investigates the ozone (O₃), ultraviolet (UV)/O₃, UV/O₃/persulfate (PS) processes for the treatment of marine oily wastewater, including degradation performance, acute toxicity evaluation, and oil flocs analysis in a benchtop circulating flow photoozonation reactor. Degradation performances have been studied by measuring the degradation rate of total oil concentrations, specific oil components (n-alkanes and polycyclic aromatic hydrocarbons (PAHs)), and total organic carbon (TOC). The results show that UV/O₃/PS could significantly enhance the removal efficiency than the other two processes, with above 90% of removal efficiency in 30 min. Acute toxicity analysis further shows that the wastewater quality is significantly improved by four-fold of the EC₅₀ of Vibrio fischeri, and the mortality of Artemia franciscana decreases from 100% to 0% after 48 h exposure. Further, the morphology and functional groups of flocs have been further characterized, showing that the floating flocs could be further degraded especially in UV/O₃/PS process. Our study further raised discussions regarding the future on-site application of O₃-based systems, based on the results generated from the treatment efficiency, toxicity, and flocs characterization. The regulation of the oxidation strength and optimization of the reaction systems could be a practical strategy for on-site marine oily wastewater treatment.

Antibiotic Resistance in the Drinking Water: Old and New Strategies to Remove Antibiotics, Resistant Bacteria, and Resistance Genes

Bacterial resistance is a naturally occurring process. However, bacterial antibiotic resistance has emerged as a major public health problem in recent years. The accumulation of antibiotics in the environment, including in wastewaters and drinking water, has contributed to the development of antibiotic resistant bacteria and the dissemination of antibiotic resistance genes (ARGs). Such can be justified by the growing consumption of antibiotics and their inadequate elimination. The conventional water treatments are ineffective in promoting the complete elimination of antibiotics and bacteria, mainly in removing ARGs. Therefore, ARGs can be horizontally transferred to other microorganisms within the aquatic environment, thus promoting the dissemination of antibiotic resistance. In this review, we discuss the efficiency of conventional water treatment processes in removing agents that can spread/stimulate the development of antibiotic resistance and the promising strategies for water remediation, mainly those based on nanotechnology and microalgae. Despite the potential of some of these approaches, the elimination of ARGs remains a challenge that requires further research. Moreover, the development of new processes must avoid the release of new contaminants for the environment, such as the chemicals resulting from nanomaterials synthesis, and consider the utilization of green and eco-friendly alternatives such as biogenic nanomaterials and microalgae-based technologies.

Investigating the Fe0/H2O systems using the methylene blue method: Validity, applications, and future directions

An innovative approach to characterize the reactivity of metallic iron (Fe⁰) for aqueous contaminant removal has been in use for a decade: The methylene blue method (MB method). The approach considers the differential adsorptive affinity of methylene blue (MB) for sand and iron oxides. The MB method characterizes MB discoloration by sand as it is progressively coated by in-situ generated iron corrosion products (FeCPs) to deduce the extent of iron corrosion. The MB method is a semi-quantitative tool that has successfully clarified some contradicting reports on the Fe⁰/H₂O system. Moreover, it has the potential to serve as a powerful tool for routine tests in the Fe⁰ remediation industry, including quality assurance and quality control (QA/QC). However, MB is widely used as a 'molecular probe' to characterize the Fe⁰/H₂O system, for instance for wastewater treatment. Thus, there is scope to avoid confusion created by the multiple uses of MB in Fe⁰/H₂O systems. The present communication aims at filling this gap by presenting the science of the MB method, and its application and limitations. It is concluded that the MB method is very suitable for Fe⁰ material screening and optimization of operational designs. However, the MB method only provides semi-quantitative information, but gives no data on the solid-phase characterization of solid Fe⁰ and its reaction products. In other words, further comprehensive investigations with microscopic and spectroscopic surface and solid-state analyses are needed to complement results from the MB method.

The Suitability of Hybrid Fe0/Aggregate Filtration Systems for Water Treatment

Metallic iron (Fe0) corrosion under immersed conditions (Fe0/H2O system) has been used for water treatment for the past 170 years. Fe0 generates solid iron corrosion products (FeCPs) which are known to in situ coat the surface of aggregates, including granular activated carbon (GAC), gravel, lapillus, manganese oxide (MnO2), pyrite (FeS2), and sand. While admixing Fe0 and reactive aggregates to build hybrid systems (e.g., Fe0/FeS2, Fe0/MnO2, Fe0/sand) for water treatment, it has been largely overlooked that these materials would experience reactivity loss upon coating. This communication clarifies the relationships between aggregate addition and the sustainability of Fe0/H2O filtration systems. It is shown that any enhanced contaminant removal efficiency in Fe0/aggregate/H2O systems relative to the Fe0/H2O system is related to the avoidance/delay of particle cementation by virtue of the non-expansive nature of the aggregates. The argument that aggregate addition sustains any reductive transformation of contaminants mediated by electrons from Fe0 is disproved by the evidence that Fe0/sand systems are equally more efficient than pure Fe0 systems. This demonstration corroborates the concept that aqueous contaminant removal in iron/water systems is not a process mediated by electrons from Fe0. This communication reiterates that only hybrid Fe0/H2O filtration systems are sustainable.

Adsorption and detoxification of pharmaceutical compounds from wastewater using nanomaterials: A review on mechanism, kinetics, valorization and circular economy

Antibiotics overuse, inappropriate conduct, and discharge have led to adverse effects on various ecosystems. The occurrence of antibiotics in surface and drinking water is a matter of global concern. It is responsible for multiple disorders, including disruption of endocrine hormones and high chronic toxicity. The hospitals, pharmaceutical industries, households, cattle farms, and aquaculture are the primary discharging sources of antibiotics into the environment. This review provides complete detail on applying different nanomaterials or nanoparticles for the efficient removal of antibiotics from the diverse ecosystem with a broader perspective. Efforts have been made to focus on the degradation pathways and mechanism of antibiotic degradation using nanomaterials. More light has been shed on applying nanostructures in photocatalysis, which would be an economical and efficient solution. The nanoscale material or nanoparticles have incredible potential for mineralizing pharmaceutical compounds in aqueous solutions at low cost, easy handling characteristics, and high efficacy. Furthermore, nanoparticles can absorb the pharmaceutical by-products and wastes at a minimum cost as they can be easily recycled. With the increasing number of research in this direction, the valorization of pharmaceutical wastes and by-products will continue to expand as we progress from old conventional approaches towards nanotechnology. The utilization of nanomaterials in pharmaceutical wastewater remediation is discussed with a major focus on valorization, energy generation, and minimization and its role in the circular economy creating sustainable development.

The mechanism of contaminant removal in Fe(0)/H2O systems: The burden of a poor literature review

The global effort to mitigate the impact of environmental pollution has led to the use of various types of metallic iron (Fe(0)) in the remediation of soil and groundwater as well as in the treatment of industrial and municipal effluents. During the past three decades, hundreds of scientific publications have controversially discussed the mechanism of contaminant removal in Fe(0)/H₂O systems, with the large majority considering Fe(0) to be oxidized by contaminants of concern. This view assumes that contaminant reduction is the cathodic reaction occurring simultaneously with Fe⁰ oxidative dissolution (anodic reaction). This view contradicts the century-old theory of the electrochemical nature of aqueous iron corrosion and hinders progress in designing efficient and sustainable remediation Fe(0)/H₂O systems. The aim of the present communication is to demonstrate the fallacy of the current prevailing view based on articles published before 1910. It is shown that properly reviewing the literature would have avoided the mistake. Going back to the roots is recommended as the way forward and should be considered first while designing laboratory experiments.

A Comprehensive Review for Groundwater Contamination and Remediation: Occurrence, Migration and Adsorption Modelling

The provision of safe water for people is a human right; historically, a major number of people depend on groundwater as a source of water for their needs, such as agricultural, industrial or human activities. Water resources have recently been affected by organic and/or inorganic contaminants as a result of population growth and increased anthropogenic activity, soil leaching and pollution. Water resource remediation has become a serious environmental concern, since it has a direct impact on many aspects of people's lives. For decades, the pump-and-treat method has been considered the predominant treatment process for the remediation of contaminated groundwater with organic and inorganic contaminants. On the other side, this technique missed sustainability and the new concept of using renewable energy. Permeable reactive barriers (PRBs) have been implemented as an alternative to conventional pump-and-treat systems for remediating polluted groundwater because of their effectiveness and ease of implementation. In this paper, a review of the importance of groundwater, contamination and biological, physical as well as chemical remediation techniques have been discussed. In this review, the principles of the permeable reactive barrier's use as a remediation technique have been introduced along with commonly used reactive materials and the recent applications of the permeable reactive barrier in the remediation of different contaminants, such as heavy metals, chlorinated solvents and pesticides. This paper also discusses the characteristics of reactive media and contaminants' uptake mechanisms. Finally, remediation isotherms, the breakthrough curves and kinetic sorption models are also being presented. It has been found that groundwater could be contaminated by different pollutants and must be remediated to fit human, agricultural and industrial needs. The PRB technique is an efficient treatment process that is an inexpensive alternative for the pump-and-treat procedure and represents a promising technique to treat groundwater pollution.

Electrochemical Degradation of Tetracycline Using a Ti/Ta2O5-IrO2 Anode: Performance, Kinetics, and Degradation Mechanism

Tetracycline (TC) is widely used in production and in life. The high volume of its use and the difficulty of its disposal have become the most important causes of environmental pollution. A suitable method needs to be found to solve this problem. In this study, the Ti/Ta₂O₅-IrO₂ electrode was characterized for its surface morphology and crystal composition. The electrochemical catalytic ability of the Ti/Ta₂O₅-IrO₂ electrode was investigated using LSV and CV tests. The electrochemical degradation of tetracycline (TC) in water with a Ti/Ta₂O₅-IrO₂ anode was investigated. The main influence factors, such as current density (2.5–10 mA/cm²), electrode spacing (20–40 mm), initial TC concentration (20–80 mg/L) and initial solution pH (4.74–9.48) were analyzed in detail and their influences on reaction kinetics was summed up. The removal rate increased along with the increasing current density, decreasing initial TC concentration and decreasing of electrode distance under the experimental conditions. The optimum pH was 4.74. UV–vis, total organic carbon (TOC) and high-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses were used to reveal the mechanism of TC degradation. Nine main intermediates were identified, and the degradation pathways were proposed. A new insight has been postulated for the safe and efficient degradation of TC using the Ti/Ta₂O₅-IrO₂ electrode.

Characterizing the impact of MnO2 addition on the efficiency of Fe0/H2O systems

The role of manganese dioxide (MnO₂) in the process of water treatment using metallic iron (Fe⁰/H₂O) was investigated in quiescent batch experiments for t ≤ 60 d. MnO₂ was used as an agent to control the availability of solid iron corrosion products (FeCPs) while methylene blue (MB) was an indicator of reactivity. The investigated systems were: (1) Fe⁰, (2) MnO₂, (3) sand, (4) Fe⁰/sand, (5) Fe⁰/MnO₂, and (6) Fe⁰/sand/MnO₂. The experiments were performed in test tubes each containing 22.0 mL of MB (10 mg L⁻¹) and the solid aggregates. The initial pH value was 8.2. Each system was characterized for the final concentration of H⁺, Fe, and MB. Results show no detectable level of dissolved iron after 47 days. Final pH values varied from 7.4 to 9.8. The MB discoloration efficiency varies from 40 to 80% as the MnO₂ loading increases from 2.3 to 45 g L⁻¹. MB discoloration is only quantitative when the operational fixation capacity of MnO₂ for Fe²⁺ was exhausted. This corresponds to the event where adsorption and co-precipitation with FeCPs is intensive. Adsorption and co-precipitation are thus the fundamental mechanisms of decontamination in Fe⁰/H₂O systems. Hybrid Fe⁰/MnO₂ systems are potential candidates for the design of more sustainable Fe⁰ filters.

UV Stimulated Manganese Dioxide for the Persulfate Catalytic Degradation of Bisphenol A

One of the most commonly produced industrial chemicals worldwide, bisphenol A (BPA), is used as a precursor in plastics, resins, paints, and many other materials. It has been proved that BPA can cause long-term adverse effects on ecosystems and human health due to its toxicity as an endocrine disruptor. In this study, we developed an integrated MnO2/UV/persulfate (PS) process for use in BPA photocatalytic degradation from water and examined the reaction mechanisms, degradation pathways, and toxicity reduction. Comparative tests using MnO2, PS, UV, UV/MnO2, MnO2/PS, and UV/PS processes were conducted under the same conditions to investigate the mechanism of BPA catalytic degradation by the proposed MnO2/UV/PS process. The best performance was observed in the MnO2/UV/PS process in which BPA was completely removed in 30 min with a reduction rate of over 90% for total organic carbon after 2 h. This process also showed a stable removal efficiency with a large variation of pH levels (3.6 to 10.0). Kinetic analysis suggested that 1O2 and SO4•− played more critical roles than •OH for BPA degradation. Infrared spectra showed that UV irradiation could stimulate the generation of –OH groups on the MnO2 photocatalyst surface, facilitating the PS catalytic degradation of BPA in this process. The degradation pathways were further proposed in five steps, and thirteen intermediates were identified by gas chromatography-mass spectrometry. The acute toxicity was analyzed during the treatment, showing a slight increase (by 3.3%) in the first 30 min and then a decrease by four-fold over 2 h. These findings help elucidate the mechanism and pathways of BPA degradation and provide an effective PS catalytic strategy.

The Suitability of Methylene Blue Discoloration (MB Method) to Investigate the Fe0/MnO2 System

The typical time-dependent decrease of the iron corrosion rate is often difficult to consider while designing Fe0-based remediation systems. One of the most promising approaches is the amendment with manganese dioxide (Fe0/MnO2 system). The resulting system is a very complex one where characterization is challenging. The present communication uses methylene blue discoloration (MB method) to characterize the Fe0/MnO2 system. Shaken batch experiments (75 rpm) for 7 days were used. The initial MB concentration was 10 mg L−1 with the following mass loading: [MnO2] = 2.3 g L−1, [sand] = 45 g L−1, and 0 < [Fe0] (g L−1) ≤ 45. The following systems where investigated: Fe0, MnO2, sand, Fe0/MnO2, Fe0/sand, and Fe0/MnO2/sand. Results demonstrated that MB discoloration is influenced by the diffusive transport of MB from the solution to the aggregates at the bottom of the test-tubes. Results confirm the complexity of the Fe0/MnO2/sand system, while establishing that both MnO2 and sand improve the efficiency of Fe0/H2O systems in the long-term. The mechanisms of water decontamination by amending Fe0-based systems with MnO2 is demonstrated by the MB method.

Ultrasensitive Detection of Tetracycline Using Boron and Nitrogen Co-Doped Graphene Quantum Dots from Natural Carbon Source as the Paper-Based Nanosensing Probe in Difference Matrices

Herein, the boron and nitrogen co-doped 0-dimensional graphene quantum dots (B,N-GQDs) with high quantum yield (QY) were synthesized via microwave-assisted hydrothermal method at 170 °C for 20 min using fresh passion fruit juice and boric acid as the starting materials. The 3–6 layers of B,N-GQDs with mean particle size of 9 ± 1 nm were then used for ultra-sensitive and selective detection of tetracycline in aqueous and biological media. The hybridization of boron and nitrogen atoms into the GQD structures increases the intensity of electronegative, resulting in the enhancement of QY to 50 ± 1%. The B,N-GQDs show their excellent analytical performance on tetracycline determination after 2 min of reaction under an optimal condition at pH 5. The linear range of 0.04–70 µM and with limits of detection (LOD) of 1 nM in phosphate buffer saline (PBS), 1.9 nM in urine and 2.2 nM in human serum are obtained. Moreover, the high selectivity of tetracycline by B,N-GQDs over the other 23 interferences is observed. The π-π interaction and electron donor-acceptor principle play pivotal roles in enhancing the ultra-sensitivity and selectivity of B,N-GQDs toward TC detection. Moreover, the B, N-GQD based paper nanosensor exhibits an excellent analytical performance on visual detection of 0.1–30 µM TC in human serum. Results of this study clearly indicate the feasibility of synthesis of B,N-GQDs derived from passion fruit juice for ultrasensitive tetracycline detection, which can open an avenue to use natural products for the preparation of environmentally benign and biocompatible carbon nanomaterials for highly sensitive detection of drugs, antibiotics, organic compounds and biomarkers.

Removal of tetracycline from an aqueous solution using manganese dioxide modified biochar derived from Chinese herbal medicine residues

Biochar (BC) derived from Chinese herbal medicine residues has been investigated for its performance as a potential adsorbent in tetracycline (TC) removal. In the present study, a chemical co-precipitation method was carried out to prepare manganese dioxide modified biochar (Mn-BC) to increase its sorption capacity. The properties of the modified biochar were characterized for further enhancing TC removal from an aqueous solution. Mn-BC was successfully synthesized and resulted in a much higher specific surface area, total pore volume and pore diameter. The sorption kinetics of TC on Mn-BC was described by the pseudo-second-order model. The sorption data of Mn-BC were fitted by Langmuir and Freundlich models. The study findings revealed a maximum adsorption capacity of Mn-BC (1:10) to TC was up to 131.49 mg/g. The adsorption process was endothermic and spontaneous. The degradation of TC was further enhanced by MnO₂ acting as an oxidizer on Mn-BC. Overall, the modified biochar derived from Chinese herbal medicine residues is a superior alternative for the removal of TC from an aqueous solution.

The removal of tetracycline, oxytetracycline, and chlortetracycline by manganese oxide-doped copper oxide: the behaviors and insights of Cu-Mn combination for enhancing antibiotics removal

Adsorption process is suitable to the advanced treatment of tetracycline antibiotics (TCs; including tetracycline (TTC), oxytetracycline (OTC), and chlortetracycline (CTC)) in poultry wastewater. In this research, Mn oxide-doped Cu oxide (MODCO) was synthesized and used for the removal of TTC, OTC, and CTC. According to the XRD and SEM analysis results, MODCO has an amorphous crystal structure and is formed by the aggregation of nano-sized particles with a uniform distribution of Cu and Mn elements. In addition, MODCO has a BET surface area of 67.7 m²/g and a pH_IEP value of 7.8. The results of batch experiments illustrated that the reaction rates for the removal of three TCs were in the order of OTC > CTC > TTC. In addition, the theoretical maximum amounts of TTC, OTC, and CTC adsorbed on MODCO were determined to be 2.90 mmol/g, 4.15 mmol/g, and 2.20 mmol/g via the Langmuir model, respectively. The optimal removal performances of TCs were achieved in the pH range of 6~9, and the coexistence of anions posed an unnoticeable effect on the removal efficiencies. The spectroscopic analysis results demonstrated that the removal mechanism of TCs was mainly attributed to surface complexation. Furthermore, a part of TCs may be decomposed by Mn oxides during the removal process according to the UV spectrogram results. Overall, MODCO has exhibited a great potential for the removal of TCs from aqueous solution.

Highly flexible, mesoporous structured, and metallic Cu-doped C/SiO2 nanofibrous membranes for efficient catalytic oxidative elimination of antibiotic pollutants

The development of inorganic membranous catalysts with both large mesopores and superb flexibility is extremely favorable for the enhancement of their catalytic oxidation activity for the degradation of antibiotic pollutants in wastewater via sulfate radical-based advanced oxidation processes; however, there still exists a huge challenge for inorganic materials to simultaneously realize these two properties. Herein, metallic copper-doped carbon/silica nanofibrous membranes (Cu@C/SiO2 NFMs) with large mesopores, superb flexibility, and robust mechanical strength were fabricated through a sol-gel electrospinning and subsequent in situ carbonization reduction method. The synthesized Cu nanoparticles were homogeneously distributed throughout the mesoporous C/SiO2 nanofiber matrix, which enabled the resultant Cu@C/SiO2 NFMs to be applied as heterogeneous catalysts, and their catalytic performance was systematically assessed through activating persulfate for the elimination of tetracycline hydrochloride (TCH) in water. The fabricated Cu@C/SiO2 NFMs provided outstanding catalytic performance towards TCH with a high removal efficiency of 95% in 40 min and a rapid removal speed of 0.054 min-1. Moreover, the membranes could be facilely recycled through being directly separated from water without any post-processing. Such a facile strategy for preparing mesoporous and flexible metal-doped inorganic nanofibrous membranes may offer novel insights for designing new types of heterogeneous catalysts for antibiotic-containing wastewater treatment or other potential applications.

Enhanced tetracycline removal by in-situ NiFe nanoparticles coated sand in column reactor

The occurrence of various antibiotics in natural waters poses an emerging environmental concern. Tetracycline (TC) is a frequently used antibiotic in human therapy, veterinary industry, and agricultural sectors. In the current study, TC removal from aqueous solutions was studied using binary Nickel/nano zero valent iron particles (NiFe nano particles) and in-situ NiFe nanoparticles coated sand (IS-NiFe). Removal of TC using bimetallic NiFe particles was optimized with help of response surface methodology (RSM). Using the optimized parameters (concentration of TC: 20 mg/L; NiFe dose: 120 mg/L; time of interaction: 90 min), 99.43 ± 0.98% removal of TC was noted. Further, IS-NiFe was packed in the column reactors and effects of different parameters like flow rate (1-3 mL/min), bed height (3-10 cm) and inlet TC concentration (20-60 mg/L) on breakthrough characteristics were examined. Under the optimized conditions the removal capacity in the column reactor was 1198 ± 40.2 mg/g using IS-NiFe. The column kinetic data were successfully fitted with Adams- Bohart and Thomas models. TC removal efficiency of IS-NiFe in column reactors was tested with TC (20 mg/L) spiked lake water, ground water, and tap water and the removal capacity was noted to be 698.55 ± 11.21, 764.17 ± 6.78, and 801.7 ± 13.26 mg/g respectively.

Removal of antibiotics from aqueous solutions by nanoparticles: a systematic review and meta-analysis

Antibiotics, as one of the emerging pollutants, are non-biodegradable compounds and long-term exposure to them may affect endocrine, hormonal, and genetic systems of human beings, representing a potential risk for both the environment and human health. The presence of antibiotics in surface waters and drinking water causes a global health concern. Many researches have stated that conventional methods used for wastewater treatment cannot fully remove antibiotic residues, and they may be detected in receiving waters. It is reported that nanoparticles could remove these compounds even at low concentration and under varied conditions of pH. The current study aimed to review the most relevant publications reporting the use of different nanoparticles to remove antibiotics from aqueous solutions. Moreover, meta-analysis was conducted on the results of some articles. Results of meta-analysis proved that different nanoparticles could remove antibiotics with an acceptable efficiency of 61%. Finally, this review revealed that nanoparticles are promising and efficient materials for degradation and removal of antibiotics from water and wastewater solutions. Furthermore, future perspectives of the new generation nanostructure adsorbents were discussed in this study.

Bi2Zr2O7 nanoparticles synthesized by soft-templated sol-gel methods for visible-light-driven catalytic degradation of tetracycline

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. Bi₂Zr₂O₇, an effective photocatalyst, but no studies on its photodegradation of TC could be found in literature. In this study, Bi₂Zr₂O₇ was synthesized by three soft templated sol-gel methods. Three synthesized Bi₂Zr₂O₇ catalysts have different structures, morphologies and band gaps. The Bi₂Zr₂O₇ nanoparticles synthesized with citric acid as the template (BZO-3) had a larger specific surface area (30.7 m²/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, Bi₂Zr₂O₇ nanoparticles were found effective as photocatalyst for TC photodegradation by visible light.

Eggshell Membrane-Templated MnO2 Nanoparticles: Facile Synthesis and Tetracycline Hydrochloride Decontamination

Taking advantages of reticular proteins and reductive groups on the surface, eggshell membrane (ESM) was selected to synthesize MnO₂ nanoparticles from potassium permanganate through a super simple way in which ESM acted as both template and reductant. This process avoided harsh reaction conditions or complicated aftertreatments and thus owned the merits of green synthesis, handy operation, low cost, and easy purification. The ESM-templated MnO₂ nanoparticles (MnO₂ NPs/ESM) were characterized, and the content of nanomaterials on the template was tested. MnO₂ NPs/ESM showed a good capacity for decontamination of tetracycline hydrochloride (TCH). The macroscopical materials can be separated easily by taking the membrane out to stop the degradation instead of centrifugation or filtration. It was studied that 72.27% of TCH (50 mg/L) was decontaminated in 20 min by 0.1920 g/L MnO₂ nanoparticles, and removal efficiency could reach 83.10% after 60 min under buffered condition. The kinetics was studied with or without buffer, and it was concluded that the degradation process followed a pseudo-second-order model. The facile synthesis of materials and effective degradation would facilitate the nano-MnO₂-based decontamination applications.

Degradation of tetracycline in a schorl/H2O2 system: Proposed mechanism and intermediates

Schorl could perform as an extremely promising catalyst for decomposing tetracycline hydrochloride (TC) due to its high degradation efficiency, low cost, chemical stability, easy recovery and repeatable utilization. Comparisons of TC degradation indifferent systems showed that schorl/H₂O₂ system exhibited the optimum pollutant elimination and TOC removal efficiencies. Kinetics and possible mechanisms of TC degradation were clarified. The OH generated on the schorl surface and O₂^-/HO₂ were the main reactive species responsible for TC oxidation. Six possible intermediates were identified, and possible transform mechanisms and pathways were explored. Active radicals were inclined to attack the CC double bond, dimethylamino and phenolic moieties of TC molecular. The principal intermediate products were generated through N-demethylation, oxidation and rearrangement.