Electron Donor-acceptor Interactions Research Articles

A novel cellulose/lignin/montmorillonite ternary hybrid aerogel for efficiently adsorptive removal of antibiotics from water

A novel fully environmental-friendly organic–inorganic ternary hybrid aerogel (LN/MMT@cellulose), composed of lignin (LN), montmorillonite (MMT), and cellulose, was designed and simply fabricated. LN/MMT@cellulose was employed for the adsorptive removal of typical antibiotic ciprofloxacin (CIP) in water. The combined MMT and LN reinforce the mechanical properties of the cellulose aerogel and notably enhance the selective adsorption capacity toward CIP in the presence of various inorganic and organic matters. LN/MMT@cellulose still presents good adsorption ability toward CIP even at the CIP concentration as low as 0.002 mmol/L in various actual water sources. With the combination of the adsorption kinetics, isotherms, and thermodynamic study as well as the various spectroscopic characterizations before and after adsorption, the mechanisms of LN/MMT@cellulose in CIP adsorption were investigated in detail. Various interactions were involved in CIP adsorption by this composite aerogel under different pH levels, causing the evident pH dependence of its adsorption capacity, specifically, the cation exchange and electrostatic attractions associated with the chelation, π-π electron donor–acceptor interaction, and the ordinary hydrogen bondings were dominant at pH < 6.0, but the complexation and negatively charged assisted hydrogen bondings played the key roles under neutral and alkaline conditions. LN/MMT@cellulose had a slight loss in adsorption ability toward CIP and sustained physicochemical structural stabilities, even after seven adsorption–deadsorption cycles. In addition to CIP, LN/MMT@cellulose could be efficiently used for the adsorptive removal of two other popular antibiotics, namely, tetracycline, and trimethoprim. The said vital characteristics of LN/MMT@cellulose confirmed it is a promising material for the adsorptive removal of antibiotics in practical water treatment.

Fixed bed column experiments using cotton gin waste and walnut shells-derived biochar as low-cost solutions to removing pharmaceuticals from aqueous solutions

Acetaminophen (ACT), sulfapyridine (SPY), ibuprofen (IBP) and docusate (DCT) are pharmaceuticals with widespread usage that experience incomplete removal in wastewater treatment systems. While further removal of these pharmaceuticals from wastewater effluent is desired prior to beneficial reuse, additional treatment technologies are often expensive and energy intensive. This study evaluated the ability of biochar produced from cotton gin waste (CG700) and walnut shells (WS800) to remove four pharmaceuticals (ACT, SPY, IBP, and DCT) from aqueous solution. Physico-chemical properties of the biochars were characterized by Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), and zeta potential. The increased pyrolysis temperature during the production of WS800 led to an increase in the specific surface area and increased dehydration of the biochar represented by the loss of the OH-group. Fixed-bed column experiments were performed to determine the difference in removal efficiency between the biochars and elucidate the effects of biochar properties on the adsorption capacity for the pharmaceuticals of interest. Results showed that CG700 had a greater affinity for removing DCT (99%) and IBP (50%), while WS800 removed 72% of SPY and 68% of ACT after 24 h. Adsorption was influenced by the solution pH, surface area, net charge, and functional groups of the biochars. The mechanisms for removal included pore filling and diffusion, hydrophobic interactions, hydrogen bonding, and π-π electron donor acceptor interactions. To conduct predictive modeling of the column breakthrough curves, the Thomas, Adams-Bohart, and Yoon-Nelson models were applied to the experimental data. Results demonstrated that these models generally provided a poor fit for the description of asymmetrical breakthrough curves. Overall, the results demonstrate that biochars from cotton gin waste and walnut shells could be used as cost-effective, environmentally friendly alternatives to activated carbon for the removal of pharmaceuticals from aqueous solutions.

CeO2-g-C3N4 S-scheme heterojunctions for enhanced photocatalytic performance: Effects of surface C/N ratio on photocatalytic and adsorption properties

In this work, novel CeO2–C-g-C3N4 S-scheme heterojunctions with significantly enhanced photocatalytic performance were prepared for the first time by a facile one-step molten KCl–LiCl method. The formation mechanism of CeO2–C-g-C3N4 was discussed, where g-C3N4 turned to C by carbonizing and the surface C content was adjusted by controlling the synthesis conditions. The photocatalytic property of the ternary composites first increased and then decreased with synthesis temperature and time. The 580 °C 4h CeO2–C-g-C3N4 exhibited the best performance towards MB (Methylene blue) and TC (Tetracyclines) degradation with a removal degree of 99.9% and 92.5%, respectively. The surface C/N ratio was a key index that influenced the photocatalytic performance, and was calculated to be 0.918–1.352 for various CeO2–C-g-C3N4 catalysts. The 580 °C 4h CeO2–C-g-C3N4 had an appropriate C/N ratio of 0.930 and a narrow band gap. The formed S-scheme 2D heterojunctions and generated C clearly promoted the separation of photo-excited e-/h+. Besides, it was indicated that e- and ·O2− were the main active species for TC photodegradation. The 580 °C 4h CeO2–C-g-C3N4 exhibited a large BET surface area, high negative zeta potential, strong π-π electron donor-acceptor interaction, and an excellent MB adsorption ability. It was evident that chemisorption on catalyst surface played an important role for adsorbing MB. The formation mechanism of CeO2–C-g-C3N4 and the effects of the surface C/N ratio on photocatalytic performance, determined in this work, offer new insights for preparing and structuring highly effective photocatalysts, which is expected to promote further photocatalytic and adsorption applications.

How PPY/CMC aerogels possess selective adsorption capacity for norfloxacin: Coupling molecular scale interpretation with experiments

In this study, the PPY/CMC aerogels showed rapid removal of norfloxacin (NOR) within 2 h with a maximum adsorption capacity of 845.7 mg/g and excellent adsorption performance in the pH range of 3–10. The exhaustive Density Functional Theory (DFT) calculations revealed that π-π electron-donor–acceptor (EDA) interactions dominated at different pH. Humic acid (HA) mainly competed with NOR for the sites of π-π EDA interactions on the adsorbent, but only slightly inhibited NOR adsorption at high concentrations due to the weak competitiveness and compensation by NOR-bridging interactions. Background ions mainly competed with NOR for electrostatically interacting sites, but ions in the lower valence state were less competitive and preferentially occupied different adsorption sites, thus hardly affecting the adsorption of NOR. The higher valence state with higher concentration of ions had increased competing ability, and although the bridging interaction can compensate some adsorption sites, it still inhibited the adsorption of NOR. The PPY/CMC aerogels had fine affinity for multiple antibiotics, and the differences in adsorption capacity were determined by the charge and structural properties of the antibiotics themselves. Moreover, excellent recyclability of PPY/CMC aerogels was confirmed after five adsorption–desorption cycles as the diminished performance from 96.8% to 83.7%. These results will help us to understand the structure-performance relationship between contaminants and PPY/CMC aerogels, and prefigure the potential of PPY/CMC aerogels as a novel adsorbent for the removal of multiple antibiotics.

Enhanced adsorption of 3,4-methylenedioxymethamphetamine by magnetic graphene oxide-polydopamine nanohybrid modified zeolitic imidazolate framework-67 and its micro-mechanism: Experiments and calculations

Exploring the structure-dependent adsorption mechanism of contaminants in wastewater is beneficial to high-efficiency adsorbents design and environmental remediation. In this study, emerging porous material of zeolitic imidazolate framework-67 (ZIF-67) has been modified by the magnetic graphene oxide-polydopamine nanohybrid (mGOP) to obtain three-dimensional ZIF-67/mGOP through an in-situ growth strategy, which was applied to adsorb 3,4-methylenedioxymethamphetamine (MDMA, “ecstasy”) in wastewater. A combination of characterizations, experiments (pH, humic acid and ion strength effect) and quantum chemical calculations revealed the microscopic adsorption mechanism involves each single component, of which the hydrogen bond (O/N…HO) and π–π electron donor acceptor (π–π EDA) interactions of mGOP endowed favourable adsorption of ZIF-67/mGOP, and mechanisms of the pore filling and Co-O chelation of ZIF-67 played synergistic effect. Such nanocomposite as a ZIFs-based adsorbent exhibited ultra-high porosity (total pore volume = 0.4033 cm3/g) and specific surface area (995.22 m2/g), revealed the heterogeneity and multilayer adsorption properties, and obtained a theoretical maximum adsorption capacity of 159.845 μg/g which higher than that of mZIF-67 alone. Overall, this work provided an effective strategy for rationally modulate ZIFs-based composites and exploration of adsorption mechanism.

Exploiting Modeling Studies for Evaluating the Potential Antiviral Activities of some Clinically Approved Drugs and Herbal Materials against SARS-CoV-2: Theoretical Studies toward Hindering the Virus and Blocking the Human Cellular Receptor

This research theoretically modeled the binding interaction of the Sars-Cov-2 (Spike protein) utilizing molecular docking with some potential repurposed antiviral medications and two botanical products (Curcumin and Quercetin). Molecular docking between the drugs and the Sars-Cov-2 proteins reflecting the pure electrostatic forces and H-bond formation is complemented with the DFT results that shed light on the electronic nature of the interactions. Moreover, DFT computations provide invaluable information about the drug reactivity indices calculated from the energies of the frontier orbitals. The DFT results indicate intermolecular electron donor-acceptor interaction besides the H-bond formation. Most of the considered medication molecules act as electron-sink candidates except EIDD-2801 (molnupiravir), the electron donor. The theoretical results show the high possibility of blocking the human cellular entry against Sare-Cov-2 via strong interaction of the drugs with its peptide sequence (β6) measured by the high binding energy of docking or weakening its activity due to the electronic donor-acceptor interactions indicated by reactivity indices computed from the frontier molecular orbitals.

Benchmarking biochar with activated carbon for immobilizing leachable PAH and heterocyclic PAH in contaminated soils

Remediation of residually contaminated soils remains a widespread problem. Biochar can immobilize polycyclic aromatic hydrocarbons (PAH). However, studies on its ability to immobilize PAH and N, S, and O substituted PAH (hetero-PAH) in real soils, and benchmarking with commercial activated carbon are missing. Here, we compared the ability of pristine biochar (BC), steam-activated biochar (SABC), and commercial activated carbon (AC) to immobilize PAH and hetero-PAH. The three carbons were tested on soils from four different contaminated sites in Austria. Different amendment rates (w/w) of the carbons were investigated (BC: 1.0, 2.5, and 5%; SABC: 0.5, 1.0, and 2.0%; AC: 1%) in batch experiments to cover meaningful ranges in relation to their performance. SABC performed better than AC, removing at least 80% PAH with the lowest application rate of 0.5%, and achieving a complete removal at an application rate of 1.0%. BC performed slightly worse but still acceptable in residually contaminated soils (40 and 100% removal at 1 and 5% amendment, respectively). The ability of BC and SABC to immobilize PAH decreased as the PAH-molar volume increased. PAH with three or more rings were preferentially removed by AC compared to SABC or BC. This can be explained by the difference in pore size distribution of the carbons which could limit the accessibility of PAH and hetero-PAH to reach sorption sites for π- π electron donor-acceptor interactions, which drive PAH and hetero-PAH sorption to carbons. Column percolation tests confirmed the results obtained in batch tests, indicating, that decisions for soil remediation can be derived from simpler batch experiments. In soil samples with 1% BC, a reduction of over 90% in the total concentration of PAH in the leached water was observed. Overall, BC and SABC were demonstrated to be valid substitutes for AC for stabilizing residually contaminated soils.

Preparation and characterization of glucose-based covalent organic polymer coated silica as stationary phase for high-performance liquid chromatography

Carbohydrate is a renewable, sustainable, hydrophilic, and biodegradable natural product, which is widely used in the field of adsorption. In this study, a glucose-based covalent organic polymer (COP) coated silica was fabricated by facile solvent knitting reaction between tetrabenzylglucose and silica-phenyl with anhydrous aluminum trichloride as catalyst, forming a core-shell stationary phase (donated as SiO2@COPBn-glu) for high performance liquid chromatography. The prepared SiO2@COPBn-glu was characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectrometry, solid-state 13C nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy, and N2 adsorption-desorption experiments. Owing to the coexistence of benzene units and alkyl, hydroxyl and ether groups in the skeleton of COPBn-glu shell, the developed chromatographic packing exhibited reversed-phase/hydrophilic interaction mixed-mode with multiple retention mechanisms, such as hydrophobic, π-π, hydrogen bonding, and electron donor-acceptor interactions. The results revealed that the SiO2@COPBn-glu column demonstrated excellent selectivity and retention behavior for both hydrophilic and hydrophobic compounds with good repeatability and stability. Meanwhile, the chromatographic performance of the prepared SiO2@COPBn-glu column was compared with a C18 column to assess the role of the coating COPBn-glu shell. Therefore, the development of the SiO2@COPBn-glu stationary phase expands the potential application of COPs in separation field.

Adsorption of nitrophenol onto a novel Fe3O4-κ-carrageenan/MIL-125(Ti) composite: process optimization, isotherms, kinetics, and mechanism

Water pollution is a dreadful affair that has incessantly aggravated, exposing our planet to danger. In particular, the persistent nitro aromatic compound like nitrophenols causes anxiety to the researchers due to their hazardous impacts, excessive usage, and removal difficulty. For this purpose, a novel multi-featured composite was constructed based on κ-Carrageenan (κ-Carr), MOF (MIL-125(Ti)), and magnetic Fe3O4 for efficient adsorptive removal of o-nitrophenol (o-NP). Interestingly, BET measurements revealed the high surface area of Fe3O4-κ-Carr/MIL-125(Ti) of about 163.27 m2/g, while VSM showed its excellent magnetic property (20.34 emu/g). The comparison study pointed out the synergistic effect between Fe3O4, κ-Carr, and MIL-125(Ti), forming a composite with an excellent adsorption performance toward o-NP. The adsorption data obeyed pseudo-second-order kinetic model, and Freundlich isotherm model was better fitted than Langmuir and Temkin. Furthermore, Langmuir verified the supreme adsorption capacity of o-NP onto Fe3O4-κ-Carr/MIL-125(Ti) since the computed qmax reached 320.26 mg/g at pH 6 and 25 °C. Furthermore, the XPS results postulated that the adsorption mechanism pf o-NP proceeded via H-bonding, π-π interaction, and electron donor–acceptor interactions. Interestingly, Fe3O4-κ-Carr/MIL-125(Ti) composite retained good adsorption characteristics after reusing for five cycles, suggesting its viable applicability as an efficient, renewable, and easy-separable adsorbent for removing nitro aromatic pollutants.

Ultra-efficient adsorption of diclofenac sodium on fish-scale biochar functionalized with H3PO4 via synergistic mechanisms

Developing safe and efficient diclofenac sodium (DS) removal technology has become a critical issue. This study synthesized the fish-scale biochar by co-pyrolysis of fish scale and phosphoric acid (H3PO4). In addition to increasing the specific surface area and pore volume of fish-scale biochar, H3PO4 assisted in the formation of Graphitic N and sp2 C, as well as reacting with C═O groups to form a significant number of phosphorus-containing groups. All these functional groups could act as major active sites for DS adsorption. Adsorption data could well fit pseudo-second-order and Langmuir models. The maximum adsorption capacity of FSB600-15 for DS was 967.1 mg g−1, which was much better than that reported in the literature. Under the synergistic effect of various mechanisms (pore-filling effect, electrostatic attraction, H-bonding, π-π, and n-π electron donor-acceptor interactions), the DS ultra-efficient adsorption on FSB600-15 was realized. Meanwhile, the DS adsorption by FSB600-15 was an endothermic, spontaneous, and entropy-increasing process. Furthermore, the DS adsorption capacity was more than 426.5 mg g−1 in the actual water, which was sufficient for practical applications.

Modification of Cu–ZnO–ZrO2 catalysts with La2O3 to quantitatively tune Cu+–Cu0 dual sites for hydrogenation of dimethyl adipate to produce 1,6-hexanediol

The strong electron donor–acceptor interaction between lanthanum and copper species retards the aggregation of the copper species, and inhibits the transformation of Cu2O to metallic Cu, thus maintaining a constant ratio of Cu+/(Cu0 + Cu+).

Frequency Changes in Terminal Alkynes Provide Strong, Sensitive, and Solvatochromic Raman Probes of Biochemical Environments.

The C≡C stretching frequencies of terminal alkynes appear in the "clear" window of vibrational spectra, so they are attractive and increasingly popular as site-specific probes in complicated biological systems like proteins, cells, and tissues. In this work, we collected infrared (IR) absorption and Raman scattering spectra of model compounds, artificial amino acids, and model proteins that contain terminal alkyne groups, and we used our results to draw conclusions about the signal strength and sensitivity to the local environment of both aliphatic and aromatic terminal alkyne C≡C stretching bands. While the IR bands of alkynyl model compounds displayed surprisingly broad solvatochromism, their absorptions were weak enough that alkynes can be ruled out as effective IR probes. The same solvatochromism was observed in model compounds' Raman spectra, and comparisons to published empirical solvent scales (including a linear regression against four meta-aggregated solvent parameters) suggested that the alkyne C≡C stretching frequency mainly reports on local electronic interactions (i.e., short-range electron donor-acceptor interactions) with solvent molecules and neighboring functional groups. The strong solvatochromism observed here for alkyne stretching bands introduces an important consideration for Raman imaging studies based on these signals. Raman signals for alkynes (especially those that are π-conjugated) can be exceptionally strong and should permit alkynyl Raman signals to function as probes at very low concentrations, as compared to other widely used vibrational probe groups like azides and nitriles. We incorporated homopropargyl glycine into a transmembrane helical peptide via peptide synthesis, and we installed p-ethynylphenylalanine into the interior of the Escherichia coli fatty acid acyl carrier protein using a genetic code expansion technique. The Raman spectra from each of these test systems indicate that alkynyl C≡C bands can act as effective and unique probes of their local biomolecular environments. We provide guidance for the best possible future uses of alkynes as solvatochromic Raman probes, and while empirical explanations of the alkyne solvatochromism are offered, open questions about its physical basis are enunciated.

Insight into atrazine removal by fallen leaf biochar prepared at different pyrolysis temperatures: Batch experiments, column adsorption and DFT calculations

The environmental pollution caused by atrazine in the agricultural production cannot be ignored. In this study, the fallen leaf biochar (LBC) was prepared at three different temperatures (500 °C, 600 °C, and 700 °C) using a simple pyrolysis method (500 LBC, 600 LBC, and 700 LBC) for atrazine adsorption. Batch experiments showed that the performance of LBC in atrazine adsorption improved with rising pyrolysis temperature, and the highest adsorption amount of 700 LBC reached 84.32 mg g−1. Kinetic and isotherm models showed that the adsorption behaviors were both monolayer and multilayer chemisorption. The findings of the characterizations (Elemental analysis, BET, XRD, Raman, FT-IR, and XPS) confirmed that the degree of aromatization determined the adsorption capacity of LBC to atrazine, and π-π electron donor-acceptor interaction was the main adsorption mechanism. Density functional theory (DFT) calculations showed that the highly aromatized biochar was more effective for atrazine adsorption, manifested as smaller molecular distances, higher adsorption energies, more stable complex structures, and stronger π-electron conjugation. In the column adsorption experiments, reducing the inlet flow rate or increasing the bed height extended the breakthrough time and exhaustion time of the breakthrough curves, and 700 LBC still showed good adsorption performance after five cycles. Overall, fallen leaf biochar as a reuse product of resource showed good potential for application in atrazine adsorption, which can be used for atrazine-contaminated water remediation.

Preparation and modification of bagasse biochar unveiling ofloxacin wastewater adsorption

ABSTRACT Currently, ofloxacin (OFX) is widely used in various medical treatment and aquaculture industries. However, its production and application produces waste which pollutes the natural environment and causes ecological damage. The application of biochar is a crucial way to remove OFX antibiotics from wastewater. In this paper, bagasse was used as the material to be pyrolyzed to obtain bagasse biochar (BC). BC was modified with HNO3 and KOH to prepare acid-modified sugarcane biochar (HBC) and alkali-modified sugarcane biochar and subsequently applied to the treatment of ofloxacin wastewater. The results showed that the adsorption capacity of HBC was 2.2 times higher than that of BC, and it had better adsorption performance. When the dosage of acid-modified biochar was 1 g/L and the initial pH of the solution was 7.0, the OFX removal rate reached 88.5% after 90 min of reaction. HBC has good stability, and the OFX removal efficiency is still up to 78.5% after 5 cycles. According to the adsorption simulation results, the adsorption of the three biochar materials is more consistent with the Freundlich adsorption model, and the simulated linear correlation coefficient is higher than 0.99. The Kfr value of HBC is 6.6042, which exhibits the highest adsorption capacity. Moreover, the three biochars exhibit better simulation results in pseudo-second-order kinetics fitting, and the linear correlation coefficients are above 0.99. The adsorption mechanism of bagasse biochar for ofloxacin in wastewater was π-π electron donor–acceptor interactions. The results show that bagasse biochar has good feasibility in the treatment of ofloxacin wastewater.

Enhanced adsorption of benzo(a)pyrene in soil by porous biochar: Adsorption kinetics, thermodynamics, and mechanisms

Soil pollution caused by polycyclic aromatic hydrocarbons (PAHs) poses a significant threat to human health and ecosystems. In this study, a novel porous biochar (PBC) was fabricated from biowastes by one-pot pyrolysis using potassium hydrogen carbonate (KHCO3) as a porogen. The as-prepared PBC was used to remove benzo(a)pyrene (BaP) in contaminated soil for the first time. The PBC obtained at 900 °C had a large surface area (2017.59 m2 g–1), which was approximately 165 times that of the original biochar (BC) (12.16 m2 g–1). The maximum adsorption capacity of BaP by the PBC reached 29.82 mg g–1, which was significantly higher than that of BC (6.94 mg g–1). Adsorption kinetics study indicated the adsorption process fitted a pseudo-second order model, and the adsorption isotherms were consistent with Langmuir model, suggesting BaP adsorption was probably a monolayer molecular adsorption process and that chemisorption was involved. Batch experiments showed that the adsorption efficiency remained high under different initial BaP concentration, initial pH values, temperature, inorganic anion, and humic acid conditions. The results suggested that pore-filling and π-π electron donor-acceptor (EDA) interactions were the main mechanisms for BaP adsorption by PBC, whereas hydrogen bonding and electrostatic interactions only partially contributed to the adsorption process. The soil leaching experiments suggested that the addition of PBC effectively reduced BaP leaching after soil remediation. This study not only provided a cost-effective biochar adsorbent for BaP-contaminated soil remediation, but also shed lights on the mechanisms about adsorption of BaP by PBC in soil.

Nitrogen-doped magnetic porous carbon material from low-cost anion-exchange resin as an efficient adsorbent for tetracyclines in water.

In this work, nitrogen-doped magnetic porous carbon material (N-MPC) was prepared through the high-temperature calcination of low-cost [Fe(CN)6]3--loaded anion-exchange resin, which was experimentally demonstrated to have significant adsorption performance for tetracycline (TC) in water. The N-MPC adsorbent with a large specific surface area (781.1 m2 g-1) was able to maintain excellent performance in a wide pH range from 4 to 10 or in high ionic strength solution. The adsorption of TC on N-MPC was found to be more consistent with the pseudo-second-order model and Langmuir adsorption model, and the maximum adsorption capacity (qm, cal) was calculated to be 603.4mg g-1. As a recoverable magnetic adsorbent, the N-MPC remained a TC removal rate higher than 70% after four adsorption cycles. The adsorption mechanism was speculated on the basis of characterizations, where pore filling, hydrogen bonding interaction, and π-π electron donor-acceptor (EDA) interaction were crucial adsorption mechanisms. A variety of antibiotics were selected for adsorption, and excellent performance was found especially for TCs, indicating that the N-MPC can be used for the efficient removal of TCs from water.

An investigation on adsorption of carbamazepine with adsorbents developed from flax shives: Kinetics, mechanisms, and desorption

In this work, adsorbents based on hydrochars and steam activated hydrochars developed from flax shives were used to adsorb carbamazepine (CBZ) from simulated contaminated water. The adsorption kinetics was investigated at various temperatures (293–313 K) and times (2–96 h). Four different kinetic models were used to analyze the experimental CBZ adsorption kinetic data. Among the tested various models, the pseudo-second-order kinetic model provided the best simulation to the kinetic data of both adsorbents with R2 of being 0.98 and above, and activation energy of 31.8 and 16.45 kJ/mol, respectively. The determined adsorption rate constant of the steam activated hydrochars ((5.88–9.09) × 10−5) was much higher than that of the hydrochars ((2.81–6.44) × 10−6). Further, X-ray photoelectron spectra and Near-Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy analysis were done before and after loading with CBZ. The results show π-π electron donor-acceptor interaction played an important role on the adsorption mechanism of CBZ on the above-mentioned adsorbents. Hydrophobic interaction also contributed while the roles of hydrogen bonding and electrostatic attraction between CBZ and adsorbents with opposite charges is insignificant. Pore filling may contribute. Desorption of CBZ from CBZ-loaded adsorbents was investigated with various organic solvents, and water at different pH (2, 6 and 10), among which ethanol was the most effective solvent to desorb CBZ. Overall, the results demonstrated that flax shives are promising feedstocks to be made into adsorbents for treatment of wastewater contaminated by antibiotics and additional pharmaceuticals.

Insight into different adsorption behaviors of two fluoroquinolone antibiotics by sediment aggregation fractions.

Sediment, consisting of different aggregation fractions, is a hotspot site for transport and transformation of various pollutants including antibiotics. However, the fate of different antibiotics in aquatic sediments mediated by sediment aggregation fraction adsorption and the mechanism behinds are still unclear. In this study, we investigated the adsorption behavior of two fluoroquinolone antibiotics (ciprofloxacin and ofloxacin) on four aggregation fractions separated from the sediment of Taihu Lake, a typical lake contaminated by antibiotics in China. The results showed that the adsorption of ciprofloxacin and ofloxacin fitted the Freundlich model, irrespective of sediment aggregation size. The adsorption of ciprofloxacin and ofloxacin was depended on the size of sediment aggregation fractions, and the macroaggregation (> 200μm) exhibited the strongest capacity, followed by large microaggregation (63-200μm), medium microaggregation (20-63μm), and small and primary microaggregation (< 20μm). This fraction size-dependent effects of sediment aggregations on antibiotic adsorption might be closely related to the differences in their specific surface areas, organic matter contents, and surface functional groups. The adsorption of ciprofloxacin and ofloxacin by sediment aggregation fractions was characterized by a combination of chemical and physical adsorptions, with the former being the dominant process. Compared with ofloxacin, ciprofloxacin could be more rapidly and easily absorbed by four sediment aggregation fractions, and more readily complexed with carboxyl groups on macroaggregation surface. The adsorption of two antibiotics by extracellular polymeric substance showed that tryptophan and tyrosine protein-like, humic-like substance on the surface of sediment could bind to both antibiotics through a complexation reaction. The π-π electron donor-acceptor interaction and hydrogen bonds were responsible for the antibiotic adsorption by sediment aggregation.

Degradation of pyrene in sediments based on the activation of peroxymonosulfate with nitrogen-doped magnetic biochar: Synergistic effect and mechanism

Pyrene (PYR) is a typical high molecular weight polycyclic aromatic hydrocarbon (HMW-PAH) with potential biotoxicity and resistance to biodegradation, and the accumulation of PYR in sediments increases the risk to ecosystems. Therefore, this study evaluated the catalytic performance of nitrogen-doped magnetic biochar-activated peroxymonosulfate system (NMBC/PMS) on PYR in sediments and elucidated its mechanism. The results showed that the degradation rate of PYR in sediments by the NMBC/PMS system reached 87% at PMS= 1 × 10−4 M, NMBC= 3.0 g/L and pH= 9, which conformed to the pseudo-first-order rate law, and the rate constant(Kobs) was 7.3 × 10−2 h−1. The high adsorption performance of NMBC was attributed to π-π electron donor-acceptor interactions (π-π EDA). The high degradation performance of NMBC/PMS system was attributed to the active sites generated by graphitization, magnetism, and electronegativity of NMBC, which were the key to activate PMS to degrade PYR. The results of X-ray photoelectron spectroscopy (XPS), quenching experiments and electron paramagnetic resonance (EPR) analysis indicated that N-doping and Fe3O4-loading on NMBC synergistically promoted the degradation of PYR. In addition, the mechanism of PYR degradation by NMBC/PMS system was investigated, indicating that SO4·-, HO·and 1O2 were the main reactive oxygen species. The excellent recoverability of NMBC showed its application potential. The NMBC/PMS system developed in this study provided a theoretical basis for a future multi-pathway synergistic degradation mechanism of PYR in sediments.

In-situ synthesis of duster-like hollow mesoporous copper silicate composites for high-efficiency adsorption of aflatoxin B1 from water

Aflatoxin B1 (AFB1) is one of the pollutants widely distributed in wastewater, which easily causes serious harm to human health and ecosystem. Mesoporous silicate materials are often used as adsorbents attributed to their well-controlled structures and high surface area. Herein, copper silicate composites (MCSCs) with novel duster-like hollow mesoporous structure were synthesized in situ on an acid-etched sepiolite substrate, and used as adsorbents for removal of AFB1 from water. The resultant MCSCs exhibited high specific surface area (439 m2/g), consequently exposing abundant functional groups (e.g., Si–OH, Cu–OH and Si–O–Cu), which contributed to improved adsorption performance. As expected, the MCSCs showed excellent AFB1 adsorption capacity, and the maximum adsorption capacity, obtained from the Langmuir model, was 24.99 mg/g. Analyses of the kinetic data revealed that the adsorption process of AFB1 onto MCSCs were fitted well with the pseudo-second-order and Weber-Moris intra-particle diffusion models. The FTIR and XPS analysis confirmed that the adsorption mechanisms were mainly electron donor-acceptor interaction and hydrogen bonding. These results in this work will provide valuable information for the development of green and efficient strategy for synthesizing other silicate materials, which are expected to applied as highly efficient adsorbents to remove AFB1 from wastewater.