High capacity adsorption of oxytetracycline by lignin-based carbon with mesoporous structure: Adsorption behavior and mechanism

Multi-interface interaction mechanism of pulp reject-based flocculants for the removal of antibiotics and its combined pollutants

The efficient removal of antibiotics and its combined pollutants is essential for aquatic environment and human health. In this study, a lignin-based organic flocculant named PRL-VAc-DMC was synthesized using pulp reject as the raw material, with vinyl acetate (VAc) and methacryloxyethyltrimethyl ammonium chloride (DMC) as the grafting monomers. A series of modern characterization methods were used to confirm the successful preparation of PRL-VAc-DMC and elucidate its polymerization mechanism. It was found that the Ph-OH group and its contiguous carbon atoms of lignin served as the primary active sites to react with grafting monomers. Flocculation experiments revealed that PRL-VAc-DMC could react with tetracycline (TC) through π-π* interaction, hydrophobic interaction, hydrogen bonding, and electrostatic attraction. With the coexistence of humic acid (HA) and Kaolin, the aromatic ring, hydroxyl, and amide group of TC could react with the benzene ring, hydroxyl group, and carboxyl group of HA, forming TC@HA@Kaolin complexes with Kaolin particles acting as the hydrophilic shell. The increase in particle size, electronegativity, and hydrophily of TC@HA@Kaolin complexes facilitated their interaction with PRL-VAc-DMC through strong interfacial interactions. Consequently, the presence of HA and Kaolin promoted the removal of TC. The synergistic removal mechanism of TC, HA, and Kaolin by PRL-VAc-DMC was systematically analyzed from the perspective of muti-interface interactions. This paper is of great significance for the comprehensive utilization of pulp reject and provides new insights into the flocculation mechanism at the molecular scale.

Biogas slurry-derived dissolved organic matter inhibited oxytetracycline adsorption by tropical agricultural soils

The increasing presence of oxytetracycline (OTC) in agricultural soils has raised global environmental concerns. We investigated the environmental behavior and fate of OTC in two types of tropical agricultural soils, focusing on the impact of dissolved organic matter (DOM) from biogas slurry. Techniques such as three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and Ultraviolet-visible spectrophotometer (UV-vis) were used to explore the adsorption mechanisms. Our findings revealed that biogas slurry-derived DOM decreased the OTC adsorption on soils and extended the time to reach adsorption equilibrium. Specifically, the equilibrium adsorption of OTC by the two soils decreased by 19.41 and 15.32 %, respectively. These adsorption processes were effectively modelled by Elovich, intraparticle diffusion, linear, and Freundlich thermodynamic models. Thermodynamic parameters suggested that OTC adsorption onto soils was spontaneous and endothermic, with competitive interactions between biogas slurry-derived DOM and OTC molecules intensifying at higher DOM concentrations. The adsorption mechanisms were governed by both physical and chemical processes. Furthermore, the presence of Ca2+ and Na+ ions significantly inhibited OTC adsorption. These insights advanced our understanding of the fate and risk of OTC in soil environments influenced by DOM, contributing to more informed agricultural and environmental management practices.

Effects of different precursors on the structure of lignin-based biochar and its ability to adsorb benzopyrene from sesame oil

Agricultural by-products of sesame are promising bioresources in food processing. This study extracted lignin from the by-products of sesame oil production, namely, the capsules and straw of black and white sesame. Using acid, alkali, and ethanol methods, 12 distinct lignins were obtained to prepare biochar, aiming to investigate both the structural characteristics of lignin-based biochar (LBB) and its ability to remove benzo[a]pyrene (BaP) from sesame oil. The results showed that white sesame straw was the most suitable raw material for preparing biochar. In terms of the preparation method, acid-extracted lignin biochar was more effective in removing BaP than alkaline or ethanol methods. Notably, WS-1LB (white sesame straw acid-extracted lignin biochar) exhibited the highest BaP adsorption efficiency (91.44 %) and the maximum specific surface area (1065.8187 m2/g), characterized by porous structures. The pseudo 2nd and Freundlich models were found to be the best fit for the adsorption kinetics and isotherms of BaP on LBB, respectively, suggesting that a multilayer adsorption process was dominant. The high adsorption of LBB mainly resulted from pore filling. This study provides an economical and highly efficient biochar adsorbent for the removal of BaP in oil.

Effective adsorption of As(V) from aqueous solution by quaternary ammonium and Zn2+ decorated lignin-based sorbent

Arsenic poses a serious harm to the natural environment and human health. Lignin decorated with quaternary ammonium and metal ion can effectively adsorb arsenic from aqueous solution. Zn2+/quaternary ammonium lignin was synthesized by quaternization and metallization from lignin with 3-Chloro-2-hydroxypropyl trimethylammonium chloride and ZnCl2. The morphology, functional groups and chemical compositions of adsorbent were identified by SEM-EDS, FTIR and XRD. The effects such as pH, initial As(V) concentration, contact time and adsorbent dosage on the adsorption capacity were investigated in batch system. The adsorption mechanism was explored by SEM-EDS, FTIR and XPS. It was shown that the adsorbent was rough and contained a large amount of quaternary ammonium and Zn2+. Zn2+/quaternary ammonium lignin exhibited much strong affinity towards As(V) with the maximum adsorption capacity of 70.38 mg·g-1 at 25 °C, oscillation rate of 180 r·min-1, pH of 5, initial As(V) concentration of 100 mg·L-1, contact time of 30 min and 1 g·L-1 Zn2+/quaternary ammonium lignin. The adsorption could be well described by Langmuir model and quasi-second-order kinetic model, indicating the monolayer homogeneous chemisorption nature. As(V) was adsorbed through electrostatic attraction of Zn2+ and ion exchange between H2AsO4- and Cl-.

Highly efficient removal of tetracyclines from water by a superelastic MOF-based aerogel: Mechanism quantitative analysis and dynamic adsorption

Metal-organic frameworks (MOFs) were promising adsorbents for removing antibiotics, but the inherent poor recyclability of MOF powders limits further application. Moreover, the dominant adsorption mechanisms and their quantitative assessment are less studied. Here, ultrahigh adsorption capacities of 821.51 and 931.87 mg g-1 for tetracycline (TC) and oxytetracycline (OTC), respectively, were realised by a novel adsorbents (biochar loaded with MIL-88B(Fe), denoted as BC@MIL-88B(Fe)), which were further immobilised in a 3D porous gelatin (GA) substrate. The obtained BCM/GA200 showed superior adsorption performance under wide pH ranges and under the interference of humic acid. Moreover, it can survive >8 cycles and even maintain high adsorption efficiency in different actual water samples. Notably, BCM/GA200 can selectively remove tetracyclines in a multivariate system containing other kinds of antibiotics and from a dynamic adsorption system. Most importantly, the results of X-ray photoelectron spectroscopy, 2D Fourier transform infrared correlation spectroscopy (2D-FTIR-COS) and density functional theory techniques revealed that (1) for TC adsorption, at pH < 4.0, the contribution of complexation was 25 %-45 %, whereas pore filling and hydrogen bonding accounted for 39 %-72 % of the total uptake. At 4.0 < pH < 10.0, the contribution of complexation increased to 60 %-82 %, whereas electrostatic attraction and π-π interaction were 4 %-13 % and 2 %-10 %, respectively. (2) For OTC adsorption, complexation was dominant at 3.0 < pH < 10.0, accounting for 55 %-86 % of the total uptake, and electrostatic attraction and π-π interactions caused 3 %-10 % and 3 %-15 %, respectively. (3) At pH > 10.0, pore filling dominated TC and OTC adsorption. Finally, the reaction sequences of the main adsorption mechanisms were also probed by 2D-FTIR-COS. This work solves the poor recyclability of MOF powders and provides a mechanistic insight into antibiotic removal by MOFs.

In-situ preparation of lignin/Fe3O4 magnetic spheres as bifunctional material for the efficient removal of metal ions and methylene blue

In this paper, magnetic composite of lignin/Fe3O4 spheres were synthesized via a straightforward one-step in-situ solvothermal method showing good capacity for adsorbing heavy metal ions and dyes. The physicochemical properties of lignin/Fe3O4 spheres are analyzed using a range of techniques such as SEM, XRD, FTIR, VSM, TG, and BET. Lignin/Fe3O4 spheres exhibited high adsorption capacities of 100.00, 353.36 and 223.71 and 180.18 mg/g for Cu (II), Ni (II) and Cr (VI) metal ions and methylene blue (MB) with equilibrium attained within 60 min. After the recycling experiments, lignin/Fe3O4 spheres still possesses excellent superparamagnetic properties and displays high adsorption capacity. The lignin/Fe3O4 spheres are an efficient and continuous adsorbent to remove heavy metal ions of Cu (II), Ni (II), Cr (VI) and cationic dyes of methylene blue in wastewater, which proves the great potential in practical pollutants treatment applications for water systems.

Self-Assembled Aminated and TEMPO Cellulose Nanofibers (Am/TEMPO-CNF) Aerogel for Adsorptive Removal of Oxytetracycline and Chloramphenicol Antibiotics from Water

Antibiotics are used for the well-being of human beings and other animals. Detectable levels of antibiotics can be found in pharmaceutical, municipal, and animal effluents. Therefore, the treatment of antibiotic contaminated water is of great concern. In this study, we fabricated a sustainable aminated/TEMPO cellulose nanofiber (Am/TEMPO-CNF) aerogel to remove oxytetracycline (OTC) and chloramphenicol (CAP) from synthetic wastewater. The prepared aerogel was characterized using different analytical techniques such as elemental analysis, FTIR, TGA, SEM-EDS, and N2 adsorption-desorption isotherms. The characterization techniques confirmed the presence and interaction of quaternary amine -[NR3]+ and -COOH groups on Am/TEMPO-CNF with OTC and CAP, which validates the successful modification of Am/TEMPO-CNF. The adsorption process of the pollutants was examined as a function of solution pH, concentrations, reaction time, and temperatures. The maximum adsorption capacity was 153.13 and 150.15 mg/g for OTC and CAP, respectively. The pseudo-second order (PSO-2) was well fitted to both OTC and CAP, confirming the removal is via chemisorption. Hydrogen bonding and electrostatic attraction have been postulated as key factors in facilitating OTC and CAP adsorption according to spectroscopic studies. Energetically, the adsorption was spontaneous and endothermic for both pollutants. In conclusion, the efficient removal rate and excellent reusability of Am/TEMPO-CNF indicate the strong potential of the adsorbent for antibiotics' removal.

Multifunctional carboxymethyl cellulose/graphene oxide/polyaniline hybrid thin film for adsorptive removal of Cu(II) and oxytetracycline antibiotic from wastewater

The antibiotics and metal ions in the contaminated water bodies must be removed using appropriate methods for sustainable development. In this study, the multifunctional carboxymethyl cellulose/graphene oxide/polyaniline (CMC/GO/PANI) hybrid thin film was synthesized and utilized for adsorptive scavenging of (Cu(II) and oxytetracycline (OTC) from wastewater. The prepared thin films' morphology, chemical compositions, functionality, and surface charge were analyzed by well-known physicochemical techniques. The adsorption process of the selected model pollutants was examined as a function of reaction time, Cu(II), and OTC solution pH, concentrations, and temperatures. Results showed that CMC/GO/PANI hybrid thin film had higher Cu(II) and OTC adsorption than CMC, GO/CMC, and PANI/CMP thin films due to the multifunctional synergetic effect. The adsorption kinetic data were fitted to the pseudo-second-order model. Redlich-Peterson isotherm model well interpreted Cu(II) and OTC scavenging equilibrium data. Energetically, the adsorption was spontaneous and endothermic for both pollutants. The multifunctional CMC/GO/PANI thin film was recycled and reused seven times during adsorption-desorption cycles. The study outcomes demonstrated that CMC/GO/PANI thin film could be reused multiple times for large-scale wastewater purification.