Synthesis of Fe3O4/Polyacrylonitrile Composite Electrospun Nanofiber Mat for Effective Adsorption of Tetracycline

Poly(acryloyl hydrazide)-grafted cellulose nanocrystal adsorbents with an excellent Cr(VI) adsorption capacity

In this study, we prepared poly(acryloyl hydrazide) (PAH)-grafted cellulose nanocrystal (CNC-PAH) particles via the atom transfer radical polymerization method for application to Cr(VI) adsorption. The closely-packed PAH chains grafted on the cellulose nanocrystal (CNC) surface provide a high density of amine groups that can adsorb Cr(VI) through strong electrostatic, hydrogen bonding and chelating interactions. CNC-PAH exhibited the optimum Cr(VI) adsorption capacity at the solution pH = 3, where its electrostatic attraction with Cr(VI) was maximized. Cr(VI) was chemisorbed in CNC-PAH by following the Langmuir isotherm mechanism (homogeneous monolayer adsorption). The Cr(VI) adsorption kinetics of CNC-PAH was controlled predominantly by intra-particle diffusion resistance imparted by the PAH shell layer. Thermodynamic analysis revealed that Cr(VI) adsorption of CNC-PAH is a spontaneous and endothermic process. Importantly, CNC-PAH grafted with the higher M_w (∼50 kg mol^-1) PAH exhibited a rapid Cr(VI) adsorption rate and remarkably high Cr(VI) adsorption capacity (∼457.6 mg g^-1 at 298.15 K), exceeding those of previously reported adsorbents owing to its numerous Cr(VI)-adsorptive amine groups provided by the closely-packed grafted PAH polymers. Furthermore, CNC-PAH showed excellent reusability to maintain its high adsorption ability during repeated adsorption-desorption cycles owing to the covalently binding nature of the PAH polymers.

Polymer-modified mesoporous silica microcubes (P@MSMCs) for the synergistic oxidative entrapment of Ag(i), Ti(iv), and Zn(ii) from natural river water

Herein, we demonstrate a hydrothermal route to the one-pot synthesis of polymeric mesoporous silica microcubes (P@MSMCs) for the adsorption of heavy metal ions. During the synthesis of P@MSMCs from column silica gel, the roles and combination of the polymer and an etchant were characterized. Moreover, the porosity of P@MSMCs was tailored by adjusting the reaction temperature between 75 °C and 200 °C. The characterization through UV, FTIR, FESEM, XRD, BET, and EDX techniques exhibited that P@MSMCs have a well-ordered mesoporous structure with cubic morphology. The P@MSMCs had a diameter of 2 μm, with an average pore volume and pore size of 0.69 cm3 g-1 and 10.08 nm, respectively. The results indicated that the P@MSMCs have excellent adsorption capacity for Ag(i), Ti(iv), and Zn(ii) due to the formation of an aggregated complex. These aggregations led to affordable density difference-based separation of these metal ions through centrifugation, filtration or simple decantation. The removal efficiencies for Ag(i), Ti(iv), and Zn(ii) were observed to be 520, 720, and 850 mg g-1, respectively. The kinetic studies demonstrated that the adsorption performance fitted well to the pseudo-second-order kinetic model. The as-synthesized P@MSMCs were stable in the wide pH range of 4-8. Significantly, the recycling or reuse results displayed effective adsorption performance of these P@MSMCs for up to 5 cycles. The adsorption results obtained herein will promote the development of similar strategies for the removal of heavy metal ions from natural water.

The effective adsorption of tetracycline onto zirconia nanoparticles synthesized by novel microbial green technology

Pseudomonas aeruginosa bacteria have been used in this study for zirconia nanoparticles synthesis through green technology for adsorption driven bioremediation of tetracycline from wastewater. The characterization of synthesized nano zirconia has been performed by employing dynamic light scattering, field emission-transmission electron microscopy, energy dispersive X-ray, X-ray diffraction, fourier transform infrared spectroscopy, and point of zero charge analysis. The zirconia nanoparticles have shown average particle size ~15 nm, monoclinic and tetragonal crystal structure with 6.41 nm of crystallite size, the presence of elemental zirconium and oxygen, and the occurrence of functional groups like O-Zr-OH, Zr-O-Zr and Zr-O bonds. The zirconia nanoparticles mediated adsorption of tetracycline has been found to be effective at solution pH 6.0 and in a very less contact time 15 min. Strong electrostatic interaction between zwitterionic form of tetracycline and protonated surface of zirconia nanoparticles is the governing adsorption mechanism in this study. The kinetic study has been performed on the basis of the tetracycline adsorption process revealing that the adsorption phenomenon follows pseudo-second order kinetic, further suggesting chemisorption of tetracycline over zirconia nanoparticles. The Langmuir isotherm model has been found to be the best fitted model among the all isotherm models indicating the involvement of monolayer uptake of tetracycline on the surface of zirconia nanoparticles. Moreover, the maximum tetracycline adsorption capacity of zirconia nanoparticles calculated by the Langmuir isotherm model is close to 526.32 mg/g. This finding is quite reasonable to accept that zirconia nanoparticle may be used as an alternative adsorbent to mitigate the tetracycline contamination in wastewater.

BSA loaded bead-on-string nanofiber scaffold with core-shell structure applied in tissue engineering

Beaded nanofiber is a promising fibrous structure could act as drug delivery system with sustained drug release for regulating cell behaviors used in tissue engineering. Poly (L-lactic acid-co-ε-caprolactone) (PLCL) beaded nanofiber with core-shell structure (130 ± 30 nm) was fabricated and bovine serum albumin (BSA) was encapsulated into the inner layer. The surface morphology and characteristic were evaluated by scanning electron microscopy (SEM), inverted fluorescence microscopy and water contact angle test. Degradation analyses suggested that PLCL/BSA core-shell @ beaded nanofibers could maintain the fibrous framework during 3 weeks. The biocompatibility was investigated by in vitro cultivation of human mesenchymal stem cells (hMSCs) on the surface of PLCL/BSA core-shell @ beaded nanofibers. The proliferation of hMSCs was tested using alamar blue reagent and the spreading morphology of cells was observed by SEM. Corresponding results suggested that beaded nanofibers with core-shell structure could effectively support the attachment and proliferation of cells. PLCL beaded nanofiber with core-shell structure would work as a promising candidate for drug release system and tissue engineering.

Multifunctional conjugated microporous polymers with pyridine unit for efficient iodine sequestration, exceptional tetracycline sensing and removal

In this work, two multifunctional conjugated microporous polymers (CMP-LS7-8) were obtained via the Pd-catalyzed Suzuki coupling reactions of 2,4,6-tris(4-bromophenyl)pyridine with two aromatic borates. The Brunauer-Emmett-Teller (BET) surface areas of CMP-LS7-8 were calculated to be 507 and 2028 m² g^-1. CMP-LS7-8 exhibit excellent volatile iodine adsorption about 2.77 and 5.29 g g^-1, respectively, and outstanding reversible adsorption. High adsorption capacity should be attributed to an integrated effect by excellent porous characteristics, effective sorption sites, and expanded π-conjugated network. In addition, this platform integrated two functions of sensing and adsorption of tetracycline (TC) into one material. The excellent luminescence of CMP-LS7-8 can be effectively quenched by TC, which demonstrates they can be acted as new sensitive and selective fluorescence probes toward TC. Simultaneously, CMP-LS7-8 also display high adsorption ability of TC. The adsorption kinetics of TC suggested that the process of adsorption followed a pseudo-second-order model, and the adsorption behaviour of these polymers fitted with the Langmuir model. These results suggest that CMP-LS7-8 posess high volatile iodine capture and exceptional TC detection and removal performance, which can be promising candidates for environmental remediation.

ZIF-mediated N-doped hollow porous carbon as a high performance adsorbent for tetracycline removal from water with wide pH range

The N-doped porous carbon (NPC) and N-doped hollow porous carbons (NHPC-1 and NHPC-2) were fabricated using ZIF-8 and its composites (resorcinol and formaldehyde coated ZIF-8, ZIF-8@RF and tannic acid coated ZIF-8, ZIF-8@TA) as precursors via high-temperature pyrolysis and their applications for removing tetracycline (TC) from water were investigated. The various technologies, including SEM, TEM, FT-IR, Raman, N₂ adsorption-desorption, XRD and XPS were used to characterize the morphology, textual property, phase and microstructure of three porous carbon materials. The adsorption isotherms and kinetics of TC on three porous carbon materials were fitted well with Langmuir model and pseudo-2nd order model, respectively. In terms of the Langmuir model, the maximum TC adsorption capacities on the NPC, NHPC-1 and NHPC-2 were 180.2, 284.9 and 518.1 mg g^-1 at 25 °C, respectively. The excellent performance of NHPC-2 for TC removal is mainly attributed to the suitable pore size distribution and pore volume, high nitrogen contents and large amounts of defects. High TC adsorption was achieved in 3-10 pH range and hardly affected by humic acid. TC adsorption on NHPC-2 is spontaneous and endothermic process. The NHPC-2 kept excellent TC adsorption capacity even after eight cycles, showing its good repeatability. Our result indicates that the MOF-mediated N-doped hollow porous carbon is promising for the TC removal from aqueous media.

Enhanced adsorption performance and regeneration of magnetic Fe3O4 nanoparticles assisted extracellular polymeric substances in sulfonamide-contaminated water

It is still unclear about the superiority of the nanoscale Fe₃O₄-assisted extracellular polymeric substances (EPS) compared to traditional EPS and its application feasibility in sulfonamide-contaminated aqueous system. This study reported eco-friendly and reusable EPS/Fe₃O₄ was applied in the sulfonamide-contaminated water treatment, including sulfamethoxazole (SMX), sulfamerazine (SM1), sulfamethazine (SM2) and sulfadiazine (SDZ), respectively. EPS/Fe₃O₄ exhibited the adsorption performance of 77.93%, 74.13%, 65.62%, and 56.64% for SMX, SM1, SM2 and SDZ, respectively, increased by 7.93%, 19.02%, 13.78% and 9.93% compared to traditional EPS. The initial pH value tuned adsorption performance via varying existing species of each sulfonamides. The adsorption process could be well fitted by Freundlich and pseudo-second-order kinetics models. Moreover, the multiple evidences from SEM, FTIR, zeta potential and XRD explained the adsorption mechanisms (i.e., chemisorption, ion exchange, hydroxyl group and hydrophobicity). Desorption and recycle adsorption experiments demonstrated the well regeneration ability of EPS/Fe₃O₄ as biosorbent (67.12% adsorption performance for SMX after five adsorption-desorption cycles), suggesting EPS/Fe₃O₄ was considered as a superior choice for sulfonamide-contaminated water treatment compared to the unrecyclable EPS.

Recent progress in the design and synthesis of nanofibers with diverse synthetic methodologies: characterization and potential applications

The advancements of nanotechnology, particularly nanomaterials science, have produced a broad range of nanomaterials including nanofibers, nanorods, nanowires and etc., which have been technically and practically examined over various applications.

Controlled Fabrication of K2Ti8O17 Nanowires for Highly Efficient and Ultrafast Adsorption toward Methylene Blue

Advanced adsorbents need high adsorption rate and superior adsorption capability to clean up organic methylene blue (MB) from wastewater. We prepared K₂Ti₈O₁₇ nanowires grown along the [0 1 0] direction with a one-step hydrothermal method. The K₂Ti₈O₁₇ nanowires with tens of nanometers in diameter and tens of micrometers in length were achieved with smooth surfaces and twisted wire-like morphology. The K₂Ti₈O₁₇ nanowires exhibit high uptake capacity of ∼208.8 mg·g^-1 in the MB removal under equilibrium pH = 7. The adsorption equilibrium of MB onto the K₂Ti₈O₁₇ adsorbent is achieved with a 97% removal rate of MB within only ∼21 min, which is the shortest adsorption time among the recently reported inorganic adsorbents toward MB. The adsorption process has a good agreement with the well-known pseudo-second-order kinetic model (k₂ = 0.2) and the Langmuir isotherm model. Fourier transform infrared measurements suggest that the adsorption can be assigned to the hydrogen bonding and electrostatic attraction between MB and K₂Ti₈O₁₇. This ultrafast removal ability is due to the larger (0 2 0) interplanar spacing and zigzag surface structure of the nanowires, which provide abundant active adsorption sites. Thermodynamic parameters reflect the spontaneous, exothermic, and feasible uptake of MB. Besides, K₂Ti₈O₁₇ nanowires enjoy high adsorptive ability for chromium(VI) ions and photocatalytic removal toward NO. This work highlights the great significance of K₂Ti₈O₁₇ nanowires as a low-cost promising material used for the adsorptive elimination of organic contaminations in fast water purification on a large scale.

The efficient removal of methylene blue from water samples using three-dimensional poly (vinyl alcohol)/starch nanofiber membrane as a green nanosorbent

In the present study, a simple, fast, and economical method was introduced to eliminate methylene blue from dye wastewater water using a non-toxic, inexpensive, stable, and efficient adsorbent. The poly (vinyl alcohol) (PVA)/starch hydrogel nanofiber membrane with high surface area and the three-dimensional structure was fabricated in water via electrospinning strategy, and the cross-linking reaction was done by thermal treatment. The characterization of the nanofibers was carried out using Fourier-transform infrared spectrometer (FT-IR) and field-emission scanning electron microscopy (FE-SEM), and the cross-linked PVA/starch nanofiber was applied as a membrane for the removal of methylene blue (MB). The recovery of MB was performed by methanol solution containing 5% (v/v) HCl. Langmuir isotherm model successfully described the adsorption of MB on nanosorbent, and the maximum adsorption capacity (q_m) was 400 mg g^-1. Also, the kinetic of adsorption was well fitted by the pseudo-second-order model. In this study, because of the high stability of fabricated membrane (based on the tensile testing), it can be used as a filter for the fast separation of MB (cationic dye) and methyl orange (MO, anionic dye). Graphical abstract.

Study on Preparation and Separation and Adsorption Performance of Knitted Tube Composite β-Cyclodextrin/Chitosan Porous Membrane

In order to obtain membranes with both organic separation and adsorption functions, knitted tube composite β-cyclodextrin/chitosan (β-CD/CS) porous membranes were prepared by the non-solvent induced phase separation (NIPS) method using CS and β-CD as a membrane-forming matrix, glutaraldehyde as crosslinking agent to improve water stability, and knitted tube as reinforcement to enhance the mechanical properties. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), contact angle, water flux, bovine serum albumin (BSA) rejection and tensile test were carried out. The FTIR demonstrated that the β-CD and CS had been successfully crosslinked. With the crosslinking time increased, the membrane structure became denser, the contact angle and the rejection rate increased, while the water flux decreased. The strength and elongation at a break were 236 and 1.7 times higher than these of bare β-CD/CS porous membranes, respectively. The strength of crosslinking membranes increased further. The adsorption performance of composite membranes was investigated for the removal of phenolphthalein (PP) from aqueous solution. The adsorption process followed the Langmuir isotherm model, and the kinetic behavior was accorded with the Double constant equation and the Elovich equation. The adsorption mechanism could be explained by the synergistic effect of host-guest interaction from β-cyclodextrin, non-uniform diffusion and porous network capture.

Metal Ion-Bridged Forward Osmosis Membranes for Efficient Pharmaceutical Wastewater Reclamation

Membrane performance in separation relies largely on the membrane properties. In this study, metal ions of Cu²⁺, Co²⁺, and Fe³⁺ are used individually as a bridge to develop forward osmosis (FO) membranes via a clean complexation reaction. A metal ion-bridged hydration layer is formed and endows the membrane with a more hydrophilic and smoother surface, higher fouling resistance, and renewability. These improvements make the newly developed membranes superior to the pristine one with better FO performances. The Fe³⁺-bridged membrane produces water fluxes increased up to 133% (FO mode) and 101% (PRO mode) compared with the pristine membrane against DI water with 0.5-2.0 M MgCl₂ as the draw solution. The Fe³⁺-bridged membrane can efficiently reclaim pharmaceuticals such as trimethoprim and sulfamethoxazole from their dilute solutions with good water permeability and a high pharmaceutical retention. This membrane also exhibits a stronger renewability with water flux restored to 98% of its original value after 20 h experiments in trimethoprim-containing water treatment. This study provides a facile and clean approach to develop highly efficient FO membranes for wastewater reclamation and pharmaceutical enrichment.

Electrospun spongy zero-valent iron as excellent electro-Fenton catalyst for enhanced sulfathiazole removal by a combination of adsorption and electro-catalytic oxidation

In this study, a highly active electro-Fenton catalyst, spongy zero-valent iron (ZVI), has been developed at first via in-situ synthesis of ZVI nanoparticles (NPs) on an electrospun three-dimensional (3D) nanofiber network. The spongy ZVI effectively overcame the defects of easy aggregation of ZVI NPs and ferric sludge accumulation during the electro-catalytic process. Then, a three-dimensional electro-Fenton (3D-EF) system using the as-fabricated spongy ZVI as particle catalytic electrodes was designed, which presented a significant synergistic effect of adsorption and electro-catalytic oxidation on the enhanced removal of a widely used antibiotic, sulfathiazole (STZ) from water. Adsorption experiments demonstrated that the spongy ZVI had a relative high adsorption affinity towards STZ with about 50% of the total removal within 240 min, and the adsorption equilibrium was reached in 570 min. Hydroxyl radical (OH) was produced in the 3D-EF system with spongy ZVI catalyst, and almost 100% STZ was removed within 5 min. Reactive oxygen species analysis verified that OH was mainly responsible for the STZ degradation. Based on intermediates identified by a liquid chromatography-tandem mass spectrometry (LC-MS/MS), three pathways for the electro-Fenton oxidative degradation of STZ were proposed.

Preparation of polydopamine-modified zeolitic imidazolate framework-8 functionalized electrospun fibers for efficient removal of tetracycline

This work shows a simple and environmental friendly methodology to obtain a kind of polydopamine coating assisted preparation of zeolitic imidazolate framework-8 (ZIF-8) functionalized composite electrospun fiber (ZIF-8/PDA/PAN fibers) adsorbent. Characterization of the composite electrospun fiber was carried out and the tetracycline (TC) adsorption properties from water were also studied in detail. At the same time, principle adsorption mechanisms were thoroughly studied. The results show that the pseudo-second-order model can simulate sorption kinetics well, while sorption isotherms are able to significantly conform to the Freundlich model, and the adsorption capacity of the fibers can reach 478.18 mg/g at 298 K. In addition, the Weber-Morris model indicates that the processes of adsorption of ZIF-8/PDA/PAN fibers for TC involve surface adsorption as well as intraparticle diffusion, and the limit rate step is not only the intraparticle diffusion but also the binding of the sorbate to the sorbent. Moreover, the adsorption efficiency toward TC by ZIF-8/PDA/PAN fibers still reached over 85% of its initial adsorption capacity after five adsorption/desorption cycles, which signified that the adsorbents is stable and recyclable. This work indicates that the obtained ZIF-8/PDA/PAN fibers have practical application prospects in the field of antibiotic adsorption.

Antibiotic removal by agricultural waste biochars with different forms of iron oxide

Pollution by antibiotics has become a serious threat to public health. In this study, agricultural waste, corn husk, in the form of biochar, was utilized for antibiotic removal from wastewater. Two kinds of iron-loaded biochars, impregnation-pyrolysis biochar (IP) and pyrolysis-impregnation biochar (PI), were synthesized to adsorb the typical antibiotics tetracycline (TC) and levofloxacin (LEV). PI contained amorphous hydrated iron oxide, whereas the major component of IP was γ-Fe2O3. Compared with IP, PI had a much higher adsorption capacity for both TC and LEV. This was because PI could provide more -OH, especially -OHads, to serve as the adsorption sites. In comparison with TC, -OH was prone to combine with LEV. FT-IR and XPS results indicated that the mechanisms of LEV adsorption included hydrogen bonding, F-replacement, electrostatic attraction and bridging bidentate complexation. TC adsorption may involve complexation, hydrogen bonding and electrostatic attraction.

Highly efficient immobilization of NZVI onto bio-inspired reagents functionalized polyacrylonitrile membrane for Cr(VI) reduction

To provide superior substrates and determine the specific species of immobilized nano zero-valent iron (NZVI) system, polyacrylonitrile (PAN) membrane was functionalized by bio-inspired polydopamine (PDA) and poly(_l-DOPA) (PDOPA) for efficient immobilization of NZVI. The synthesized composites were denoted as PAN/PDA-NZVI (PPN) and PAN/PDOPA-NZVI (PON), respectively. Analyses of XRD, SEM/EDS and XPS show that the aggregation and release of iron nanoparticles had been successfully controlled by improving membrane hydrophilcity and iron-chelating capacity via the graft of functionalized groups (i.e. OH and COOH) of PDA and PDOPA on PAN membrane. Both PPN and PON composites exhibited superior reactivity for Cr(VI) removal (Cr(VI) removal efficiency and reaction rate were 2.21-2.22 and 9.90-10.14 times higher than that of bare NZVI, respectively). The stability and recyclability of PPN and PON composites could be maintained over repeated cycles. Further analyses indicate that PON is more capable for Cr(VI) elimination than PPN due to the proprietary carboxyl of _l-DOPA. With the addition of 1,10-phenanthroline, membrane-chelated Fe(II) was determined to be the major species in Cr(VI) removal system, accounting for 56.9% and 53.8% with regard to PPN and PON composites, and Fe⁰ was responsible for the reduction of residual Cr(VI). Analyse of reacted composites revealed that Cr(VI) was completely converted into Cr(III), followed by formation of dominant Cr(III)/Fe(III) (oxy)hydroxides and partial desorption from NZVI reactive sites. This study suggested that both synthesized PPN and PON composites have potentials for Cr(VI)-contaminated wastewater treatment.

HPW-Anchored UiO-66 Metal-Organic Framework: A Promising Photocatalyst Effective toward Tetracycline Hydrochloride Degradation and H2 Evolution via Z-Scheme Charge Dynamics

The abolition of environmental pollutants and production of hydrogen (H₂) from water using a heterogeneous photocatalyst is a demanding science of the current scenario to solve the increasing environmental pollution and worldwide energy catastrophe in modern life. To validate this purpose, the design of low-cost and durable semiconductor-based photocatalysts with great light absorption capacity becomes the most challenging issue for researchers. Regarding this, herein the phosphotungstic acid (HPW)-anchored Zr₆O₄(OH)₄(BDC)₆ (UiO-66) metal-organic framework (MOF), i.e., HPW@UiO-66, has been prepared by a hydrothermal method and is efficient, stable, and capable of harvesting solar energy toward the degradation of tetracycline hydrochloride (TCH) and H₂ production in the presence of a sacrificial donor. The ionic interaction between HPW and UiO-66 plays a key role toward the photostability and charge-transfer mechanism of the composite and is well characterized with X-ray diffraction, UV diffuse-reflectance spectroscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. A total of 30 wt % HPW@UiO-66 shows a maximum degradation of about 87.24% of a 20 ppm TCH solution in 60 min of solar-light irradiation and about 353.89 μmol/h of H₂ production. The conduction- and valence-band potentials are well characterized with Mott-Schottky measurement and a delay charge recombination process through electrochemical impedance spectroscopy. The proposed mediator-free Z-scheme-oriented electron-hole migration route is well supported by photoluminescence, and the scavenger test well explains the better charge-carrier separation and high catalytic performance of the prepared composite. This research will bestow an advantageous blueprint to fabricate novel and challenging photocatalysts toward the photocatalytic treatment of environmental pollutants and H₂ evolution.

Test strips based on iron(iii)-impregnated alginate/polyacrylonitrile nanofibers for naked eye screening of tetracycline

Tetracycline (TC) is an inexpensive broad-spectrum antibiotic used to treat infectious diseases and to promote growth in animals. However, driven by economic interest, abuse of TC poses a serious threat to human beings, and it remains a significant challenge to create easy-to-use TC colorimetric test strips for public use. Herein, we present a strategy to prepare free-standing, nanofibrous structured test strips with tortuous porous structure and large surface area by combining polyacrylonitrile nanofibrous membranes (PAN NMs), alginate, and Fe3+. In this approach, alginate was first functionalized on the PAN NMs and then, Fe3+ was assembled into the alginate to construct a TC-sensing surface. The resultant test strips exhibited the following integrated properties: fast sensing process (10 min), low naked eye detection limit (5 μg kg-1), excellent anti-interference ability, and satisfactory reusability. Furthermore, the TC concentration-dependent color change (yellow to maroon) was quantitatively visualized by an iPhone read-out hue parameter. All the findings indicate that this intriguing approach may pave the way for versatile designing of NMs to serve as a preventive treatment for the public.

Facile photo-ultrasonic assisted reduction for preparation of rGO/Ag2CO3 nanocomposites with enhanced photocatalytic oxidation activity for tetracycline

Various antibiotics in the aquatic systems have threat the aquatic ecosystem balance and the human health. In this study, a degradation treatment method for tetracycline (TC), one of the commonly used antibiotics, was explored by using novel photocatalysts of rGO/Ag₂CO₃ under simulated sunlight, because conventional treatment methods are not efficient on the removal of TC. rGO/Ag₂CO₃ nanocomposites were synthesized via a facile photo-ultrasonic assisted reduction method. More than 90% of TC was removed by 1% (weight_rGO/weight_composites) rGO/Ag₂CO₃ within 60 min at pH = 4, which was about 1.3 times higher than that of pure Ag₂CO₃. The cycling experiments indicated that 1% rGO/Ag₂CO₃ was highly stable and could be reused for at least 5 cycles without significant deactivation to its photocatalytic activity. In addition, the effects of pH, temperature, and dosage amount of 1% rGO/Ag₂CO₃ on photocatalytic degradation were investigated. Meanwhile, the effect of ultrasonic on the degradation of TC was also investigated. This study can provide a new method for the preparation of smaller nanosized materials and photocatalysts with high activity and stability for its environmental or other applications.

Contrastive removal of oxytetracycline and chlortetracycline from aqueous solution on Al-MOF/GO granules

The presence of tetracycline antibiotics (TCS) in the water and wastewater has raised growing concern due to its potential environmental impacts; thus, their removal is of high importance. In this study, a novel aluminum-based MOF/graphite oxide (Al-MOF/GO) granule was prepared as an adsorbent for the removal of TCS including oxytetracycline (OTC) and chlortetracycline (CTC). The adsorbent was characterized via XRD, FTIR, BET, SEM, and XPS methods. The granules exhibited similar crystal structure and some new mesopores appearing compared to the parent Al-MOF/GO powder. In addition, the adsorption behavior of OTC and CTC on samples was explored as a function of initial concentration, contact time, pH, and ionic strength by means of batch experiments. The adsorption capacity reached to 224.60 and 240.13 mg·L^-1 for OTC and CTC, at C₀ = 60 mg·L^-1 as well as ambient temperature respectively. Moreover, the adsorption process of OTC and CTC on Al-MOF/GO samples can be better delineated by pseudo-second-order kinetics and Freundlich isotherm models. Besides, the adsorption mechanism over Al-MOF/GO granules was proposed, which could be ascribed to π-π interaction, cation-π bonding, and hydrogen bond. Finally, the great water stability, separation performance, and regeneration efficiency of these novel granules indicated their potential application in the OTC and CTC removals from aqueous solution.

ZIF-8-Derived Hollow Carbon for Efficient Adsorption of Antibiotics

The harmful nature of high concentrations of antibiotics to humans and animals requires the urgent development of novel materials and techniques for their absorption. In this work, CTAB (Cetyltrimethyl Ammonium Bromide)-assisted synthesis of ZIF-8 (zeolitic imidazolate framework)-derived hollow carbon (ZHC) was designed, prepared, and used as a high-performance adsorbent, and further evaluated by Langmuir and Freundlich isothermal adsorption experiments, dynamic analysis, as well as theoretical calculation. The maximum capacities of ZHC for adsorbing tetracycline (TC), norfloxacin (NFO), and levofloxacin (OFO) are 267.3, 125.6, and 227.8 mg g⁻¹, respectively, which delivers superior adsorptive performance when compared to widely studied inorganic adsorbates. The design concept of ZIF-8-derived hollow carbon material provides guidance and insights for the efficient adsorbent of environmental antibiotics.

High-efficiency adsorption of tetracycline by the prepared waste collagen fiber-derived porous biochar

Porous biochar (PBC) derived from Cr-containing waste collagen fibers was prepared by two-step pyrolysis to 800 °C (PBC-800) and alkali activation.

Induced-fit adsorption of diol-based porous organic polymers for tetracycline removal

Adsorption is recognized as one of the most efficient approaches for antibiotics removal from water. Inspired by the enzyme-substrate interaction model, we proposed induced-fit adsorption (IFA) model, and rationally designed and fabricated diol-based porous organic polymers (POPs) as adsorbents for tetracycline (TC) removal. For 2,3-naphthalenediol-based POP (NTdiol-POP), the preferable geometry of diol-groups contributed to the high binding energy with TC species and flexible methylene linkages between neighboring rigid naphthalene rings gave rise to precisely matching between TC species and adsorbents, that is, the induced-fit conformation change. As a result, NTdiol-POP exhibited a high saturated adsorption capacity of 155.8 mg g^-1. More importantly, NTdiol-POP exhibited excellent TC removal efficiencies in both concentrated solution (96% for 4 p.p.m) and trace level solution (97% for 250 p.p.b).

Production of electrospun nanofibers based on graphene oxide/gum Arabic

Over the last few years, the electrospinning technique has attracted significant attention for the production of novel nanofibrous materials. At the same time, the use of graphene oxide and the natural products extracted from plants and/or trees have become very popular in various fields of science. In this work, a new method for the production of nanofibers based on a combination of Gum Arabic (GA), as a natural tree gum exudate, PVA, as an environmentally-friendly stabilizer, and graphene oxide (GO) has been developed and characterized. SEM analysis showed fundamental differences on the surface of bare nanofibers with and without GO, and also significantly smaller fiber diameters in the case of the presence of GO (fibers <100 nm present). Raman spectroscopy confirmed and TGA analysis approximated the content of GO in the nanofibers. Adsorption of methylene blue on the produced nanofibrous membrane was about 50% higher in the presence of GO, which opens the possibility to use GO/GA/PVA fibers in several applications, for example for the removal of dyes.

Fabrication of eco-friendly nanofibrous membranes functionalized with carboxymethyl-β-cyclodextrin for efficient removal of methylene blue with good recyclability

Considering the excellent thermo-mechanical properties, chemical stability and low cost of biodegradable aliphatic-aromatic copolyesters, they are an ideal matrix when functionalized for capturing pollutants in wastewater. In this work, biodegradable poly((butylene succinate-co-terephthalate)-co-serinol terephthalate) (PBSST) copolyesters with amino side group (-NH₂) were first synthesized through copolymerization, followed by grafting carboxymethyl-β-cyclodextrin (CM-β-CD) into PBSST molecular chains via amidation reaction to prepare PBSST-g-β-CD. The corresponding nanofibrous membranes were then fabricated by electrospinning as adsorbents for efficiently removing cationic dye methyl blue (MB) from aqueous solutions. The adsorption performance of the nanofibrous membranes was fitted well with pseudo-second-order model and Langmuir isotherm model. The maximum adsorption capacity was 543.48 mg g^-1 for MB along with a removal efficiency of 98% after five regeneration cycles, indicating the high adsorption capacity and good recyclability of nanofibrous membranes. The adsorbents possess features of high adsorption capacity, eco-friendliness and easy operation, and exhibit great potential for disposing of printing-dying wastewater.

Environmentally Friendly Gelatin/β-Cyclodextrin Composite Fiber Adsorbents for the Efficient Removal of Dyes from Wastewater

In this paper, environmentally friendly gelatin/β-cyclodextrin (β-CD) composite fiber adsorbents prepared by electrospinning were used for the removal of dyes from wastewater. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and a universal materials tester were employed to characterize the internal structures, surface morphologies and mechanical strength of the composite fiber adsorbents. Additionally, the fiber was evaluated as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of the raw material ratio, pH, temperature, concentration and adsorption time were studied. The results show that the gelatin/β-CD composite fiber adsorbents possess excellent mechanical strength and high adsorption efficiency for MB. The adsorption equilibrium and adsorption kinetics are well-described by the Langmuir isotherm model and the pseudo-second-order kinetic model, respectively. The theoretical maximum adsorption capacity is 47.4 mg·g-1. Additionally, after nine successive desorption-adsorption cycles, the removal rate is still over 70%. Moreover, the gelatin/β-CD composite fiber adsorbents exhibit excellent adsorption capability for basic fuchsin, gentian violet, brilliant blue R and malachite green dyes. Therefore, owing to the characteristics of degradability, low cost and high-efficiency, the gelatin/β-CD composite fiber can be used as an efficient adsorbent for the removal of dyes from wastewater.

TiO₂ Nanotubes/Ag/MoS₂ Meshy Photoelectrode with Excellent Photoelectrocatalytic Degradation Activity for Tetracycline Hydrochloride

A novel type of TiO₂ nanotubes (NTs)/Ag/MoS₂ meshy photoelectrode was fabricated with highly oriented TiO₂ nanotube arrays grown from a Ti mesh supporting Ag nanoparticles and three-dimensional MoS₂ nanosheets. In this structure, Ag nanoparticles act as bridges to connect MoS₂ and TiO₂ and pathways for electron transfer, ensuring the abundant production of active electrons, which are the source of •O₂⁻. The TiO₂ NTs/Ag/MoS₂ mesh can be used as both photocatalyst and electrode, exhibiting enhanced photoelectrocatalytic efficiency in degrading tetracycline hydrochloride under visible light irradiation (λ ≥ 420 nm). Compared to unmodified TiO₂ NTs, the improved photoelectrocatalytic activity of the TiO₂ NTs/Ag/MoS₂ arise from the formation of Z-scheme heterojunctions, which facilitate the efficient separation of photogenerated electron-hole pairs through the Schottky barriers at the interfaces of TiO₂ NTs–Ag and Ag–MoS₂.

The preparation of carboxylic-functional carbon-based nanofibers for the removal of cationic pollutants

A simple route is presented to fabricate carboxylic-functional carbon-coated polyacrylonitrile nanofibers (oPAN@C) through preoxidation and hydrothermal carbonization. PAN fibers were firstly preoxidized to form aromatic ladder structure with the resistance to hydrothermal condition, in which more carboxyl groups were introduced on the fiber surface at the present of chitosan and citric acid. The oPAN@C composites exhibit a high adsorption capacity towards methylene blue (MB) and lead ion (Pb²⁺). The adsorption data matched the pseudo-second-order kinetic model and Langmuir model well with the maximum adsorption capacity (153.37 and 143.27 mg g^-1) for methylene blue and Pb²⁺, respectively. Moreover, oPAN@C could be regenerated easily by hydrochloric acid, and still remained high removal efficiency after 5 cycles. Therefore, oPAN@C fibers should have potential application in sewage treatment.