Poly (ethylene imine) anchored lignin composite for heavy metals capturing in water

Preparation of esterified biomass waste hydrogels and their removal of Pb2+, Cu2+ and Cd2+ from aqueous solution

The treatment of polluted water is a serious environmental problem in the world. Biomass is easily modified and can be prepared into adsorbent materials, which is expected to solve the problem of heavy metal ion adsorption in sewage. In this paper, esterified tobacco straw based hydrogels (ETS-PAA) were synthesized from waste tobacco straw biomass. The structure and thermal stability of these hydrogels were characterized by FTIR, SEM, EDS, XPS and TG. The adsorption of metal ions by the hydrogel was measured by ICP-MS. The effects of initial ion concentration, adsorption time, pH, and temperature on the heavy metal adsorption were investigated. The results showed that ETS-PAA possessed more pores, which led to a better adsorption capacity. The maximum adsorption amounts of Pb²⁺, Cu²⁺ and Cd²⁺ were 2.41 mmol·g^-1, 1.93 mmol·g^-1 and 1.77 mmol·g^-1, respectively. Finally, the adsorption mechanism and kinetics were analyzed. The adsorption was mainly accomplished by ion exchange of -COOK on the monomer chain with heavy metal ions, coordination of -OH and -CONH with heavy metal ions and interaction of ester bond, -COOH with heavy metal ions. The adsorption process was in accordance with the pseudo-second-order kinetic model and Freundlich model. The adsorption process belonged to multilayer chemisorption. This work shows that ETS-PAA was a promising material for the removal of heavy metal pollutants from aqueous solution.

Chemical and Physical Modification of Lignin for Green Polymeric Composite Materials

Lignin, a valuable polymer of natural origin, displays numerous desired intrinsic properties; however, modification processes leading to the value-added products suitable for composite materials' applications are in demand. Chemical modification routes involve mostly reactions with hydroxyl groups present in the structure of lignin, but other paths, such as copolymerization or grafting, are also utilized. On the other hand, physical techniques, such as irradiation, freeze-drying, and sorption, to enhance the surface properties of lignin and the resulting composite materials, are developed. Various kinds of chemically or physically modified lignin are discussed in this review and their effects on the properties of polymeric (bio)materials are presented. Lignin-induced enhancements in green polymer composites, such as better dimensional stability, improved hydrophobicity, and improved mechanical properties, along with biocompatibility and non-cytotoxicity, have been presented. This review addresses the challenges connected with the efficient modification of lignin, which depends on polymer origin and the modification conditions. Finally, future outlooks on modified lignins as useful materials on their own and as prospective biofillers for environmentally friendly polymeric materials are presented.

Lignin as a bioactive polymer and heavy metal absorber- an overview

As a pulping and bio-refinery by-product with phenolic chemical structure, lignin indicated high potential as natural antioxidant activity, UV blocker, antibacterial and toxic material absorbent properties. Presence of phenolic hydroxyl groups in lignin structure plays the main role of its antioxidant activity. However, lignin antioxidant power can change depending on its other structural features and functional groups like ortho-methoxy groups, -OCH₃ groups, the α-CH₂ groups, the aliphatic carbonyl groups, and the size of π-conjugated systems. Lignin in mixture with synthetic polymers, improved their thermal stability. Lignin has high UV light absorbing potential in broad-spectrum (UVA, UVB). Adding 1-5% of lignin into hand cream indicated excellent range of sun protection factor (SPF) with more than 95% UV light absorption. Lignin also indicated strong UV light protection when applied in different transparent film and protect paint, oil, and varnish from UV degradation. Lignosulfonate and other modified lignin including chemically modification, nano-particles and lignin hydrogel indicated high potential as heavy metal absorber.

Dual-Modified Lignin-Assembled Multilayer Microsphere with Excellent Pb2+ Capture

With the continuous research on lignin-based sorbents, there are still limitations in the research of spherical sorbents with a high adsorption capacity for Pb2+. In order to solve the problem of low adsorption effect, alkali lignin (AL) was modified and assembled to increase the adsorption active sites. In this work, we used dual-modified lignin (DML) as a raw material to assemble a singular lignin-based multilayer microsphere (LMM) with sodium alginate (SA) and dopamine. The prepared adsorbent had various active functional groups and spherical structures; the specific surface area was 2.14 m2/g and the average pore size was 8.32 nm. The adsorption process followed the Freundlich isotherm and the second-order kinetic model. Therefore, the LMM adsorbed Pb2+ ascribed by the electrostatic attraction and surface complexation; the adsorption capacity was 250 mg/g. The LMM showed a selective adsorption performance for Pb2+ and the adsorption capacity followed the order Pb2+ (187.4 mg/g) > Cu2+(168.0 mg/g) > Mn2+(166.5 mg/g). After three cycles, the removal efficiency of Pb2+ by the LMM was 69.34%, indicating the reproducibility of LMM.

Dual lignin-derived polymeric systems for hazardous ion removals

The functionalization of lignin derivatives for ion removals is a promising method to expedite their use in treating industrial wastewater. In this work, kraft lignin (KL) was polymerized with [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METAM) or acrylic acid (AA) in an acidic aqueous suspension system to produce cationic and anionic water-soluble lignin polymers with high molecular weights. Then, the interaction of soluble ions and KL-METAM and KL-AA was investigated using a Quartz crystal microbalance (QCM) and a vertical scan analyzer (VSA). The QCM, X-ray photoelectron spectroscopy (XPS) and contact angle measurement results showed that the adsorption efficiency of KL-AA was better than KL-METAM for ions due to the stronger electrostatic interaction, cationic π-interaction, and chelation between ions and KL-AA. Based on adsorption, sedimentation, and aggregate size analyses, the dual polymer systems of KL-AA/KL-METAM were more effective than KL-METAM/KL-AA in removing ions. Among Zn²⁺, Cu²⁺, and K⁺; Zn²⁺ interacted more effectively with polymers in all scenarios because it has higher reactivity for interacting with other elements. As the efficiency of ion removals was more remarkable than past reported findings, the system of KL-AA/KL-METAM may be a promising alternative for the removal of dissolved ions from solutions.

Copper Adsorption on Lignin for the Removal of Hydrogen Sulfide

Lignin is currently an underutilized part of biomass; thus, further research into lignin could benefit both scientific and commercial endeavors. The present study investigated the potential of kraft lignin as a support material for the removal of hydrogen sulfide (H2S) from gaseous streams, such as biogas. The removal of H2S was enabled by copper ions that were previously adsorbed on kraft lignin. Copper adsorption was based on two different strategies: either directly on lignin particles or by precipitating lignin from a solution in the presence of copper. The H2S concentration after the adsorption column was studied using proton-transfer-reaction mass spectrometry, while the mechanisms involved in the H2S adsorption were studied with X-ray photoelectron spectroscopy. It was determined that elemental sulfur was obtained during the H2S adsorption in the presence of kraft lignin and the differences relative to the adsorption on porous silica as a control are discussed. For kraft lignin, only a relatively low removal capacity of 2 mg of H2S per gram was identified, but certain possibilities to increase the removal capacity are discussed.

Hyperbranched multiple polythioamides made from elemental sulfur for mercury adsorption

Different from traditional polyethylenimine (PEI) modified Hg(ii) adsorbent materials, a novel hyperbranched polythioamide adsorbent (SPD) was prepared by using sulfur, PEI and 1,4-diethynylbenzene (DEB) as monomers.

Lignin xanthate resin-bentonite clay composite as a highly effective and low-cost adsorbent for the removal of doxycycline hydrochloride antibiotic and mercury ions in water

Natural-occurring polymer intercalated inorganic clay composites have received increasing interests in water cleanup for the features of eco-friendliness, cost-effectiveness, and availability. Herein, a new lignin xanthate resin (LXR) intercalated bentonite clay composite (LXR-BT) for the adsorption of representative organic doxycycline hydrochloride (DCH) antibiotic and inorganic Hg(II) in water was created through a feasible process. Structural characterizations by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Thermo gravimetric analysis (TG), and scanning electron microscopy (SEM) confirmed LXR was successfully intercalated between the layers of bentonite clay. The adsorption performance of DCH/Hg(II) by LXR-BT was studied in detail with varied dosage, solution pH, contact time, and initial DCH/Hg(II) concentration. The results indicated that the adsorption capacities of DCH/Hg(II) on LXR-BT were much higher than that on bentonite, and the adsorption kinetics and isotherms followed the pseudo-second-order model and Langmuir model, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirmed the adsorption mechanisms of DCH (or Hg(II)) was mainly due to π-π interaction and hydrogen bonding interaction of DCH (or the complexation of Hg(II)) with the functional groups in the LXR-BT. This study suggested the possibility of LXR-BT as a new cost-effective adsorbent for both organic and inorganic pollutants removal in water.

Peculiarities of Synthesis and Properties of Lignin⁻Silica Nanocomposites Prepared by Sol-Gel Method

The development of advanced hybrid materials based on polymers from biorenewable sources and mineral nanoparticles is currently of high importance. In this paper, we applied softwood kraft lignins for the synthesis of lignin/SiO₂ nanostructured composites. We described the peculiarities of composites formation in the sol-gel process through the incorporation of the lignin into a silica network during the hydrolysis of tetraethoxysilane (TEOS). The initial activation of lignins was achieved by means of a Mannich reaction with 3-aminopropyltriethoxysilane (APTES). In the study, we present a detailed investigation of the physicochemical characteristics of initial kraft lignins and modified lignins on each step of the synthesis. Thus, 2D-NMR, ³¹P-NMR, size-exclusion chromatography (SEC) and dynamic light scattering (DLS) were applied to analyze the characteristics of pristine lignins and lignins in dioxan:water solutions. X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) were used to confirm the formation of the lignin⁻silica network and characterize the surface and bulk structures of the obtained hybrids. Termogravimetric analysis (TGA) in nitrogen and air atmosphere were applied to a detailed investigation of the thermal properties of pristine lignins and lignins on each step of modification. SEM confirmed the nanostructure of the obtained composites. As was demonstrated, the activation of lignin is crucial for the sol-gel formation of a silica network in order to create novel hybrid materials from lignins and alkoxysilanes (e.g., TEOS). It was concluded that the structure of the lignin had an impact on its reactivity during the activation reaction, and consequently affected the properties of the final hybrid materials.

Facile one-step synthesis of functionalized biochar from sustainable prolifera-green-tide source for enhanced adsorption of copper ions

The use of biochars formed by hydrothermal carbonization for the treatment of contaminated water has been greatly limited, due to their poorly developed porosity and low content of surface functional groups. Also, the most common modification routes inevitably require post-treatment processes, which are time-consuming and energy-wasting. Hence, the objective of this research was to produce a cost-effective biochar with improved performance for the treatment of heavy metal pollution through a facile one-step hydrothermal carbonization process coupled with ammonium phosphate, thiocarbamide, ammonium chloride or urea, without any post-treatment. The effects of various operational parameters, including type of modification reagent, time and temperature of hydrothermal treatment, and ratio of modification reagent to precursor during impregnation, on the copper ion adsorption were examined. The adsorption data fit the Langmuir adsorption isotherm model quite well. The maximum adsorption capacities (mg/g) of the biochars towards copper ions followed the order of 40-8h-1.0-APBC (95.24)>140-8h-0-BC (12.52)>140-8h-1.0-TUBC (12.08)>140-8h-1.0-ACBC (7.440)>140-8h-1.0-URBC (5.277). The results indicated that biochars modified with ammonium phosphate displayed excellent adsorption performance toward copper ions, which was 7.6-fold higher than that of the pristine biochar. EDX and FT-IR analyses before and after adsorption demonstrated that the main removal mechanism involved complexation between the phosphate groups on the surface of the modified biochars and copper ions.