Highly efficient and rapid purification of organic dye wastewater using lignin-derived hierarchical porous carbon

Direct conversion of lignin-rich black liquor to activated carbon for supercapacitor electrodes

The escalating industrialization trend underscores the imperative for sustainable waste management practices. The present investigation explores a sustainable methodology for managing the waste generated from the kraft process by directly converting it into activated carbon (BLAC) through a cost-effective hydrothermal-assisted activation method. The research involved a comparative analysis of BLAC with acid-washed black liquor lignin-derived activated carbon (ABLAC) and commercial lignin-derived activated carbon (SALAC). The analysis revealed that BLAC possesses a well-developed micro and mesoporous structure, yielding a significantly higher surface area of 2277.2 m2/g as compared to ABLAC (1260 m2/g) and SALAC (1558.4 m2/g). The presence of inherent alkali in the black liquor is the main factor influencing the surface area of the BLAC. Furthermore, it demonstrated impressive electrochemical performance, showing a specific capacitance value of 871.4 F/g at 1 A/g current density, positioning it as a formidable electrode material for supercapacitor applications. The proposed direct conversion strategy will eliminate the need for high-temperature pre‑carbonization and additional lignin extraction, reducing chemical usage and presenting a greener approach.

Simple and scalable preparation of lignin based porous carbon coated nano-clay composites and their efficient removal for the diversified iodine

Here, lignin and nano-clay were used to prepare novel composite adsorbents by one-step carbonization without adding activators for radioactive iodine capture. Specially, 1D nano-clay such as halloysite (Hal), palygorskite (Pal) and sepiolite (Sep) were selected as skeleton components, respectively, enzymatic hydrolysis lignin (EHL) as carbon source, lignin based porous carbon/nano-clay composites (ELC-X) were prepared through ultrasonic impregnation, freeze drying, and carbonization. Characterization results indicated lignin based porous carbon (ELC) well coated on the surface of nano-clay, and made its surface areas increase to 252 m2/g. These composites appeared the micro-mesoporous hierarchical structure, considerable N doping and good chemical stability. Results of adsorption experiments showed that the introduction of ELC could well promote iodine vapor uptake of nano-clay, and up to 435.0 mg/g. Meanwhile, the synergistic effect between lignin based carbon and nano-clay was very significant for the adsorption of iodine/n-hexane and iodine ions, their capacity were far exceed those of a single material, respectively. The relevant adsorption kinetic and thermodynamics, and mechanism of ELC-X composites were clarified. This work provided a class of low-cost and environmentally friendly adsorbents for radioactive iodine capture, and opened up ideas for the comprehensive utilization of waste lignin and natural clay minerals.

Efficient magnetic solid-phase extraction, UPLC-MS/MS detection, and consumption assessment of five trace psychoactive substances

Wastewater-based epidemiology (WBE) has become an objective and updated surveillance strategy for monitoring and estimating consumption trends of psychoactive substances (PSs) in the population. Firstly, magnetic shrimp shell biochar-based adsorbent (DZMBC) was synthesized and employed for extraction trace PSs from municipal wastewater. Proper pyrolysis temperature and increased KOH activator content favored the pore structure and surface area, thus facilitating extraction. DZMBC delivered exceptional extraction performance such as pH stability, anti-interference property, fast magnetic separation ability, reusability, and reproducibility. Then, a method based on magnetic solid-phase extraction (MSPE) followed by ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed, validated, and utilized for the quantitative determination of five PSs in real wastewater samples. Methodological validation results indicated a favorable linearity, low method limits of detection (1.00-4.75 ng/L), and good precisions (intra-day and inter-day relative standard deviations < 4.8%). Finally, an objective snapshot of Chongqing drug use and consumption pattern was obtained. Methamphetamine (MAMP) and 3,4-methylenedioxymethamphetamine (MDMA) were the prevalent illegal drugs in local. Both concentrations and per capita consumption of MDMA displayed a change (P < 0.05) between July and September, while no statistical differences were observed for each week.

How hydrogen bonding and π-π interactions synergistically facilitate mephedrone adsorption by bio-sorbent: An in-depth microscopic scale interpretation

Mephedrone (4-methylmethcathinone, MEPH) exhibited severe ecologic hazards and health detriments. A novel deep eutectic solvent functionalized magnetic ZIF-8/hierarchical porous carbon (DMZH) with excellent selectivity, interference resistance and recyclability, was developed for the rapid adsorption of MEPH. Initially, potential adsorption sites of MEPH were predicted. Then, π-π and hydrogen bonding interactions were proposed and verified from characterizations, comparative experiments and theoretical calculations. The synergistic effects of the hydrogen bonding and π-π interactions increased the adsorption energies from -15.26 kcal⋅mol-1 to -21.83 kcal⋅mol-1, enhanced the degree of π-dissociation, enlarged the π-π isosurface area, extended the van der Waals surface mutual penetration distance, achieving stronger affinity and remarkable adsorption. Furthermore, offset (parallel-displaced) π-π stacking form existed between DMZH and MEPH. DMZH acted as the hydrogen bond donor and MEPH served as the hydrogen bond acceptor to form O-H⋯O and N-H⋯O hydrogen bonding interaction. Profiting from the synergistic effects, DMZH showed satisfactory adsorption for MEPH within 20 min with a maximum adsorption capacity of 3270.11 μg∙g-1, displayed excellent performance in wide pH range of 5∼11 and in the coexistence of multi-chemicals.

Preparation of light-colored bio-based particles by isocyanate-modified lignins and its application for tetracycline adsorption

A practical method for the preparation of lignin derivatives-light-colored bio-based particles (LC-BP) via the modification of hexamethylene diisocyanate (HDI) is presented in this work. In the mixed EtOH/H2O system, the change of solvent polarity induced the self-assembly of the lignosulfonate (LS) with the hydrophobic chromophores encapsulated inside the particles. The color of LS was reduced by the polymerization between the isocyanate groups (-N=C=O) of HDI and hydroxy groups of LS. Compared with the typical lignin-based adsorbent preparation process in the past, this is a simple, direct, and efficient preparation method and the synthetic LC-BP has good chemical stability and resistance to heat, acid and alkali. This effectively solves the problem that LS has high water solubility and is difficult to use directly for wastewater treatment. To investigate the properties, the synthetic LC-BP was characterized by SEM, specific surface area, L*a*b* (CIELAB) color space, FT-IR, XPS, and TGA. The results showed that the LC-BP exhibited obvious advantages in color reduction with a low CIE-L* value. The LC-BP exhibits a scale-like intercalation structure, which makes it a promising candidate for adsorbing tetracycline (TC) from wastewater. The conditions of pH, adsorbent dosages, adsorption time, and initial TC concentration were investigated, and the adsorption performance of LC-BP for TC was significantly better than that of conventional polyurethane particles (PP). The adsorption fitted the Langmuir model and there were hydrogen bonding, π-π conjugated binding, and electrostatic attraction during the absorption process. The adsorption capacity was up to 53.1 mg/g, and the removal rate was 67 %. The utilization of LC-BP, a low-cost, effective, and renewable resource derived from natural biomass, holds immense practical and economic potential in wastewater treatment.

Design and function of lignin/silk fibroin-based multilayer water purification membranes for dye adsorption

The treatment of dye wastewater poses a significant challenge to the sewage recycling industries. However, the reduction of secondary pollution resulting from the membrane residues, to maintain high performance, remains a considerable obstacle. A novel approach for the fabrication of multilayer nanofiber structures using a layer-by-layer electrostatic spinning technique with biological materials was reported in this study. Incorporating the chemical adsorption advantages of lignin nanofiber and the physical adsorption advantages of silk fibroin (SF) nanofiber enabled the full realization of excellent dye interception performance. A comparative analysis was conducted on the lignin derived from eucalyptus, pine, and straw to determine the most suitable option. Notably, eucalyptus lignin exhibited superior antimicrobial properties. The adsorption of crystal violet by eucalyptus lignin/SF membrane was consistent with the Freundlich isotherm model and the pseudo-second-order kinetic model, revealing a chemisorption mechanism involving Π-Π conjugation, hydrogen bonding, and the binding of anions and cations. The lignin/SF membrane exhibited a retention rate exceeding 99.5 % for crystal violet, methylene blue, and brilliant green dyes. Furthermore, it demonstrated efficacy in retaining heavy metal ions, including cadmium and copper. The original biomass material imparts the property of rapid degradation to a multilayer membrane that can be used as an effective and eco-friendly water purification material.

Green conversion of waste PET into magnetic Ni0·4Fe2·6O4/(Fe,Ni)@carbon nanostructure for adsorption and separation of dyes from aqueous media

A nanostructured core-shell composite (Ni0·4Fe2·6O4/(Fe,Ni)@carbon, NFC) comprising magnetic nano-cores encapsulated with graphitic shells (≈80 wt%) is prepared by facile and clean mechanochemical-molten salt processing approach using waste PET; providing a specific surface area of 201.9 m2 g-1, well-developed mesopores, and ferromagnetic behavior characterized by the coercivity value of 149 Oe. NFC is utilized as a high-performance adsorbent for the removal of organic dyes from their aqueous solutions. Moreover, the magnetic performance of NFC enables the facile collection of the exhausted adsorbent out of the purified water. Performances of NFC for the removal of crystal violet dye (CV), methyl orange (MO) and rhodamine B (Rh B) from their aqueous solutions are systematically investigated under different environmental conditions including the adsorbent dosage and dye concentration, as well as the solution pH and temperature, where an impressive CV removal capacity of 201.6-243.8 mg g-1 is recorded for a wide pH range of 2-10. Mechanism and kinetics involved in the adsorption process are investigated by studying the adsorption isotherms and thermodynamics. The dye adsorption of the nanocomposite material is confirmed to follow the pseudo-second-order kinetic model combined with the Langmuir isotherm model, exhibiting an excellent spontaneous and exothermic monolayer adsorption capacity of around 153 mg g-1 (for MO) for the fresh adsorbent and around 89 mg g-1 after three adsorption-regeneration cycles.

Heterostructured Ag@MOF-801/MIL-88A(Fe) Nanocomposite as a Biocompatible Photocatalyst for Degradation of Reactive Black 5 under Visible Light

Heterostructured Ag@MOF-801/MIL-88A(Fe) nanocomposite was synthesized through template effects in metal-organic frameworks (MOFs). MIL-88A(Fe) was fabricated on a MOF-801 template using the internal extended growth method (IEGM) via polyvinylpyrrolidone (PVP) as the structure-director agent to create the MIL-88A(Fe)-on-MOF-801 heterostructure. The MOF-801/MIL-88A(Fe) heterostructure was used as a template for the formation of Ag nanoparticles (NPs) inside it via a double solvents method (DSM) combined with a photoreduction route (PR). To characterize synthesized samples to a high level of detail, PXRD, FT-IR, EDX, N2 adsorption-desorption isotherms, TEM, DRS, PL, EIS, and Mott-Sckottky measurements were used. The resulting Ag@MOF-801/MIL-88A(Fe) nanocomposite demonstrated the highest photocatalytic activity of 91.72% for the degradation of Reactive Black 5, after 30 min under visible light irradiation.

Application of Fe-MOFs in Photodegradation and Removal of Air and Water Pollutants: A Review

Photocatalytic technology has received increasing attention in recent years. A pivotal facet of photocatalytic technology lies in the development of photocatalysts. Porous metal-organic framework (MOF) materials, distinguished by their unique properties and structural characteristics, have emerged as a focal point of research in the field, finding widespread application in the photo-treatment and conversion of various substances. Fe-based MOFs have attained particular prominence. This review explores recent advances in the photocatalytic degradation of aqueous and gaseous substances. Furthermore, it delves into the interaction between the active sites of Fe-MOFs and pollutants, offering deeper insights into their mechanism of action. Fe-MOFs, as photocatalysts, predominantly facilitate pollutant removal through redox processes, interaction with acid sites, the formation of complexes with composite metal elements, binding to unsaturated metal ligands (CUSs), and hydrogen bonding to modulate their respiratory behavior. This review also highlights the focal points of future research, elucidating the challenges and opportunities that lie ahead in harnessing the characteristics and advantages of Fe-MOF composite catalysts. In essence, this review provides a comprehensive summary of research progress on Fe-MOF-based catalysts, aiming to serve as a guiding reference for other catalytic processes.

Deep insight into selective adsorption behavior and mechanism of novel deep eutectic solvent functionalized bio-sorbent towards methcathinone: Experiments and DFT calculation

This work designed and synthesized novelly selective, highly efficient and friendly environmental biochar nanomaterial (ZMBC@ChCl-EG) by screening suitable deep eutectic solvent (DES) as the functional monomer via Density Functional Theory (DFT). The prepared ZMBC@ChCl-EG achieved the highly efficient adsorption of methcathinone (MC) and exhibited excellent selectivity as well as good reusability. Selectivity analysis concluded that the distribution coefficient value (K_D) of ZMBC@ChCl-EG towards MC was 3.247 L/g, which was about 3 times higher than that of ZMBC, corresponding to stronger selective adsorption capacity. The studies of isothermal and kinetics indicated that ZMBC@ChCl-EG had an excellent adsorption capacity towards MC and the adsorption was mainly chemically controlled. In addition, DFT was used to calculate the binding energies between MC and each component. The binding energies were -10.57 kcal/mol for ChCl-EG/MC, -3.15∼-9.51 kcal/mol for BCs/MC, -2.33 kcal/mol for ZIF-8/MC, respectively, suggesting that DES played a major role in enhancing methcathinone adsorption. Lastly, the adsorption mechanisms were revealed by variables experiment combined with characterizations and DFT calculation. The main mechanisms were hydrogen bonding and π-π interaction.

Preparation and Adsorption Properties of Lignin/Cellulose Hydrogel

With the development of global industry, industrial wastewater pollution has caused serious environmental problems, and the demand for green and sustainable adsorbents is increasingly strong in the society. In this article, lignin/cellulose hydrogel materials were prepared using sodium lignosulfonate and cellulose as raw materials and 0.1% acetic acid solution as a solvent. The results showed that the optimal adsorption conditions for Congo red were as follows: an adsorption time of 4 h, a pH value of 6, and an adsorption temperature of 45 °C. The adsorption process was in line with the Langmuir isothermal model and a quasi-second-order kinetic model, which belonged to single molecular layer adsorption, and the maximum adsorption capacity was 294.0 mg/g. The optimal adsorption conditions for Malachite green were as follows: an adsorption time of 4 h, a pH value of 4, and an adsorption temperature of 60 °C. The adsorption process was consistent with the Freundlich isothermal model and a pseudo-second-order kinetic model, which belonged to the chemisorption-dominated multimolecular layer adsorption with the maximum adsorption capacity of 129.8 mg/g.

Enrichment of the flavonoid fraction from Eucommia ulmoides leaves by a liquid antisolvent precipitation method and evaluation of antioxidant activities in vitro and in vivo

Eucommia ulmoides leaves originate from the dry leaves of the Eucommia ulmoides plant. Flavonoids are the main functional components of Eucommia ulmoides leaves. Some flavonoids such as rutin, kaempferol and quercetin are rich in Eucommia ulmoides, and they have outstanding antioxidant efficacy. However, the poor water solubility significantly affects the bioavailability of flavonoids. In this study, we used a liquid antisolvent precipitation (LAP) method to enrich the main flavonoid fractions in Eucommia ulmoides leaves, and prepared nanoparticles by the LAP method to increase flavonoids' solubility and antioxidant properties. The technological parameters were optimized by Box-Behnken Design (BBD) software and were displayed as follows: (1) total flavonoids (TFs) concentration: 83 mg mL^-1; (2) antisolvent-solvent ratio: 11; (3) deposition temperature: 27 °C. Under optimal processing conditions, the purity and recovery rate of TFs were 88.32% ± 2.54% and 88.08% ± 2.13%, respectively. In vitro experiments showed that the radical scavenging IC₅₀ values for DPPH, ABTS, hydroxyl radicals and superoxide anions were 16.72 ± 1.07, 10.76 ± 0.13, 227.68 ± 18.23 and 335.86 ± 15.98 μg mL^-1, respectively. In vivo studies showed that the obtained purified flavonoid (PF) (100, 200, 400 mg kg^-1) treatment is able to improve CCl₄-induced liver and kidney damage through adjusting, superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) levels. These results demonstrated that the LAP method is capable of extracting TFs from Eucommia ulmoides leaves with high bioaccessibility.

Construction of Cu-N coordination into natural biopolymer lignin backbone for highly efficient and selective removal of cationic dyes

Here, a Cu²⁺-doped lignin-based adsorbent (Cu-AL) was fabricated via the amination and Cu²⁺-doping of industrial alkali lignin for massive and selective adsorption of cationic dyes azure B (AB) and saffron T (ST). The Cu-N coordination structures endowed Cu-AL with stronger electronegativity and higher dispersity. Through the electrostatic attraction, π-π interaction, H-bonding, and Cu²⁺ coordination, the adsorption capacities of AB and ST reached up to 1168 and 1420 mg g^-1, respectively. The pseudo-second-order model and Langmuir isotherm model were more relevant to the AB and ST adsorption on Cu-AL. Based on the thermodynamic study, the adsorption progresses were endothermic, spontaneous, and feasible. The Cu-AL maintained high removal efficiency to dyes after 4 reuses (>80%). Importantly, the Cu-AL could efficiently remove and separate AB and ST from dye mixtures even in real time. All the above characteristics demonstrated that Cu-AL was an excellent adsorbent for fast wastewater treatment.

Adsorption Studies on the Removal of Anionic and Cationic Dyes from Aqueous Solutions Using Discarded Masks and Lignin

The carbon materials derived from discarded masks and lignin are used as adsorbent to remove two types of reactive dyes present in textile wastewater: anionic and cationic. This paper introduces the results of batch experiments where Congo red (CR) and Malachite green (MG) are removed from wastewater onto the carbon material. The relationship between adsorption time, initial concentration, temperature and pH value of reactive dyes was investigated by batch experiments. It is discovered that pH 5.0-7.0 leads to the maximum effectiveness of CR and MG removal. The equilibrium adsorption capacities of CR and MG are found to be 232.02 and 352.11 mg/g, respectively. The adsorption processes of CR and MG are consistent with the Freundlich and Langmuir adsorption models, respectively. The thermodynamic processing of the adsorption data reveals the exothermic properties of the adsorption of both dyes. The results show that the dye uptake processes follow secondary kinetics. The primary adsorption mechanisms of MG and CR dyes on sulfonated discarded masks and alkaline lignin (DMAL) include pore filling, electrostatic attraction, π-π interactions and the synergistic interactions between the sulphate and the dyes. The synthesized DMAL with high adsorption efficiency is promising as an effective recyclable adsorbent for adsorbing dyes, especially MG dyes, from wastewater.

Recent Advances in Carbon-Based Materials for Adsorptive and Photocatalytic Antibiotic Removal

Antibiotics have been a primary environmental concern due to their widespread dispersion, harmful bioaccumulation, and resistance to mineralization. Unfortunately, typical processes in wastewater treatment plants are insufficient for complete antibiotic removal, and their derivatives in effluent can pose a threat to human health and aquatic communities. Adsorption and photocatalysis are proven to be the most commonly used and promising tertiary treatment methods. Carbon-based materials, especially those based on graphene, carbon nanotube, biochar, and hierarchical porous carbon, have attracted much attention in antibiotic removal as green adsorbents and photocatalysts because of their availability, unique pore structures, and superior physicochemical properties. This review provides an overview of the characteristics of the four most commonly used carbonaceous materials and their applications in antibiotic removal via adsorption and photodegradation, and the preparation of carbonaceous materials and remediation properties regarding target contaminants are clarified. Meanwhile, the fundamental adsorption and photodegradation mechanisms and influencing factors are summarized. Finally, existing problems and future research needs are put forward. This work is expected to inspire subsequent research in carbon-based adsorbent and photocatalyst design, particularly for antibiotics removal.

Advances in Micro-/Mesopore Regulation Methods for Plant-Derived Carbon Materials

In recent years, renewable and clean energy has become increasingly important due to energy shortage and environmental pollution. Selecting plants as the carbon precursors to replace costly non-renewable energy sources causing severe pollution is a good choice. In addition, owing to their diverse microstructure and the rich chemical composition, plant-based carbon materials are widely used in many fields. However, some of the plant-based carbon materials have the disadvantage of possessing a large percentage of macroporosity, limiting their functionality. In this paper, we first introduce two characteristics of plant-derived carbon materials: diverse microstructure and rich chemical composition. Then, we propose improvement measures to cope with a high proportion of macropores of plant-derived carbon materials. Emphatically, size regulation methods are summarized for micropores (KOH activation, foam activation, physical activation, freezing treatment, and fungal treatment) and mesopores (H3PO4 activation, enzymolysis, molten salt activation, and template method). Their advantages and disadvantages are also compared and analyzed. Finally, the paper makes suggestions on the pore structure improvement of plant-derived carbon materials.