Development of eco-friendly CO2-responsive cellulose nanofibril aerogels as "green" adsorbents for anionic dyes removal

Reactive Blue MEBF 222 dye and textile wastewater treatment using metal-doped cobalt and nickel perovskites by batch and column adsorption process

Water contamination is a serious issue that has an impact on the whole globe. In the current work, adsorption technique was used to remove synthetic Reactive Blue MEBF 222 textile dye utilizing Cd-doped Co (Co1 - xCd1.5xFeO3), Zn-doped Co (Co1 - xZn1.5xFeO3), Cr-doped Co (Co1 - xCr1.5xFeO3), Zn-doped Ni (Ni1 - xZn1.5xFeO3), and Cr-doped Ni (Ni1 - xCr1.5xFeO3) perovskites, synthesized by sol-gel auto-combustion approach. According to the findings of batch adsorption studies, maximum adsorption was observed at pH 3 (45.62 mg/g), 0.01 g/50 ml dosage (36.67 mg/g), 60 min (14.31 mg/g), 100 ppm dye concentration (47.41 mg/g), and 308 K (35.96 mg/g) for Co1 - xCd1.5xFeO3; at 3 pH (42.94 mg/g), 0.01 g/50 ml dosage (35.33 mg/g), 60 min (12.88 mg/g), 100 ppm dye concentration (40.52 mg/g), and 308 K (31.31 mg/g) for Co1 - xZn1.5xFeO3; at 2 pH (38.82 mg/g), 0.01 g/50 ml dosage (32.20 mg/g), 60 min (11.98 mg/g), 100 ppm dye concentration (33.54 mg/g), and 308 K (29.34 mg/g) for Co1 - xCr1.5xFeO3; at 2 pH (34.97 mg/g), 0.01 g/50 ml dosage (30.41 mg/g), 60 min (10.46 mg/g), 100 ppm dye concentration (27.19 mg/g), and 308 K (26.12 mg/g) for Ni1 - xZn1.5xFeO3; and at 2 pH (31.22 mg/g), 0.01 g/50 ml dosage (25.04 mg/g), 60 min (9.48 mg/g), 100 ppm dye concentration (21.73 mg/g), and 308 K (23.61 mg/g) for Ni1 - xCr1.5xFeO3. The pseudo-second-order model showed good fitness for adsorption kinetic data. Electrolytes, detergents/surfactants, and heavy metal ions had a substantial impact on the adsorption potential. The column adsorption experiments demonstrated optimal bed height, flow rate, and intake dye concentration to be 3 cm, 1.8 ml/min, and 70 mg/l, respectively, in the column experiment. With an adsorption capacity of 44.1 mg/g, reactive blue (RB) 222 dye was able to achieve its maximum adsorption. Detailed desorption of RB 222 dye was also achieved. The novelty of this adsorption method lies in its eco-friendliness, ease of handling, and cost-effectiveness.

Urchin-like CO2-responsive magnetic microspheres for highly efficient organic dye removal

CO2-responsive materials have emerged as promising adsorbents for the remediation of refractory organic dyes-contaminated wastewater without the formation of byproducts or causing secondary pollution. However, realizing the simultaneous adsorption-separation or complete removal of both anionic and cationic dyes, as well as achieving deeper insights into their adsorption mechanism, still remains a challenge for most reported CO2-responsive materials. Herein, a novel type of urchin-like CO2-responsive Fe3O4 microspheres (U-Fe3O4 @P) has been successfully fabricated to enable ultrafast, selective, and reversible adsorption of anionic dyes by utilizing CO2 as a triggering gas. Meanwhile, the CO2-responsive U-Fe3O4 @P microspheres exhibit the capability to initiate Fenton degradation of non-adsorbable cationic dyes. Our findings reveal exceptionally rapid adsorption equilibrium, achieved within a mere 5 min, and an outstanding maximum adsorption capacity of 561.2 mg g-1 for anionic dye methyl orange upon CO2 stimulation. Moreover, 99.8% of cationic dye methylene blue can be effectively degraded through the Fenton reaction. Furthermore, the long-term unresolved interaction mechanism of organic dyes with CO2-responsive materials is deciphered through a comprehensive experimental and theoretical study by density functional theory. This work provides a novel paradigm and guidance for designing next-generation eco-friendly CO2-responsive materials for highly efficient purification of complex dye-contaminated wastewater in environmental engineering.

Microwave synthesis of amino-functionalized MCM-41 from coal gasification fine slag for efficient bidirectional adsorption of anionic and cationic dyes

Coal based solid waste has been recognized as a sustainable raw material for the preparation of high added value materials for wastewater treatment. In this paper, a preparation route was designed for the rapid, efficient, and low-cost preparation of MCM-41 zeolite using coal gasification fine slag as raw material. Functionalization modification of MCM-41 was carried out by grafting amino groups on its surface to improve its application performance. Moreover, the prepared functionalized material is used for bidirectional adsorption of anionic and cationic dyes. The experimental results indicate that MCM-41 zeolite with highly ordered pore structure was rapidly prepared using the advantages of fast heating and strong permeability of microwave synthesis method, with a specific surface area of up to 862.03 m2/g. Amine functionalized MCM-41 exhibits strong adsorption capacity for both cationic and anionic dyes, with maximum adsorption capacities for methylene blue and Congo red being 292.40 mg/g and 354.61 mg/g, respectively. The study of adsorption kinetics and adsorption mechanism indicate that the adsorption process is mainly controlled through chemical adsorption, including electrostatic attraction, hydrogen bonding, and π-π interactions. The results of this study will provide useful references for the use of coal based solid waste to prepare functional materials for the treatment of organic wastewater.

Hierarchical Porous Aerogels With Multiple Adsorptive Interactions for Dye Wastewater Purification

Aerogels present a huge potential for removing organic dyes from printing and dyeing wastewater (PDW). However, the preparation of aerogels with multiple dye adsorption capabilities remains a challenge, as many existing aerogels are limited to adsorbing only a single type of dye. Herein, a composite aerogel (CG/T-rGO) with the addition of carboxymethyl chitosan, gelatin and tannic acid reduced graphene oxide (T-rGO) was synthesized by freeze-drying technology. The electrostatic interactions between dye molecular and GEL/CMCS (CG) networks, as well as the supramolecular interactions (H-bonds, electrostatic interactions and π-π stacks) between T-rGO, have endowed the aerogel with the ability to adsorb multiple types of dye, such as methylene blue (MB) and methyl orange (MO). Results exhibited that the prepared CG/T-rGO aerogel possessed strong mechanical strength and a porous 3D network structure with a porosity of 96.33 %. Using MB and MO as adsorbates, the adsorption capacity (88.2 mg/g and 66.6 mg/g, respectively) and the mechanism of the CG/T-rGO aerogel were investigated. The adsorption processes of aerogel for MB and MO were shown to follow the pseudo-second-order kinetic model and Langmuir isotherm model, indicating the chemical adsorption of a monolayer. The proposed aerogel in this work has promising prospects for dye removal from PDW.

Development of novel amino-ethyl chitosan hydrogel for the removal of methyl orange azo dye model

The present study introduces a new and straightforward method for the amination of Chitosan. This method involves coupling Chitosan (CS) with 2-chloroethylamine (ENH2) in a single step to produce an amino-ethyl Chitosan derivatives with increased amine group content (CS-ENH2) using click chemistry. The resulting derivatives were then crosslinked using Glutaraldehyde to form amino-ethyl Chitosan Schiff bases. The novel amino-ethyl Chitosan Schiff bases were subsequently utilized as adsorbents for the removal of Methyl Orange (MO) dye from aqueous solutions using a batch technique, and the performance of the produced Schiff bases was compared with that of the native Chitosan Schiff base. The CS-ENH2 adsorbents show improved adsorption capacity up to 300% of the native Chitosan Schiff base with almost double removal rate. The adsorption temperature has a positive impact in general while almost 100% of MO removed at 60 °C using CS-ENH2 adsorbents compared with 66% of the native Chitosan Schiff base adsorbent. The adsorption pH shows a negative impact on the MO removal percent. That effect reduced sharply using the CS-ENH2 adsorbents with higher amination degree while the MO removal percent almost being constant over a wide range of pH; 2.0-7.0. The agitation speed has the same positive effect over all the adsorbents. However, the rate of MO removal percent decreased with increase the agitation speed up to 250 rpm. The experimental findings demonstrated that the highest percentage of MO dye removal was achieved under the conditions of pH 2.0, a temperature of 60 °C, agitation speed of 250 rpm, and adsorption duration of 90 min. These Schiff bases were subsequently characterized using advanced analytical techniques including Fourier Transform Infrared spectroscopy, Thermal analysis (TGA and DSC), and Scanning Electron Microscopy.

Compressible polydopamine modified pomelo peel powder/poly(ethyleneimine)/κ-carrageenan aerogel with pH-tunable charge for selective removal of anionic and cationic dyes

In this work, a novel biomass-based aerogel, polydopamine decorated pomelo peel powder/polyethyleneimine/κ-carrageenan (PPEKC) aerogel, was developed for dye wastewater treatment. The as-prepared PPEKC aerogel possessed a robust structure and good compressible resilience. As expected, this aerogel presented remarkable efficacy in eliminating both anionic and cationic dyes. The experimental maximum adsorption capacities were 2016.7 mg g-1 for congo red (CR) at pH = 5 and 1176.6 mg g-1 for methylene blue (MEB) at pH = 11, following with ultra-fast adsorption rates. The adsorption kinetics followed the pseudo-second-order model. The adsorption isotherms exhibited a stronger alignment with the Langmuir isotherm model for CR at 308 K and MEB at 288, 298, 308 K. The Freundlich isotherm model yielded a suitable fit for the adsorption of CR at 288 and 298 K. Thermodynamic analyses indicated that the removal of CR and MEB was spontaneous and endothermic. The adsorption mechanisms involved electrostatic interactions, π-π interactions, and hydrogen bonds. Intriguingly, it could achieve bidirectional selective adsorption of anionic and cationic dyes in the designed pH values, due to pH-tunable surface charge. Additionally, it also exhibited favorable reusability and antibacterial activity. Therefore, the as-prepared PPEKC aerogel could be a promising biosorbent for dye wastewater treatment.

Fe-pillared montmorillonite functionalized chitosan/gelatin foams for efficient removal of organic pollutants by integration of adsorption and Fenton degradation

A Fe-pillared montmorillonite (Fe-MMT) functionalized bio-based foam (Fe-MMT@CS/G) was developed by using chitosan (CS) and gelatin (G) as the matrix for high-efficiency elimination of organic pollutants through the integration of adsorption and Fenton degradation. The results showed that the mechanical properties of as-obtained foam were strengthened by the addition of certain amounts of Fe-MMT. Interestingly, Fe-MMT@CS/G displayed efficient adsorption ability for charged pollutants under a wide range of pH. The adsorption processes of methyl blue (MB), methylene blue (MEB) and tetracycline hydrochloride (TCH) on Fe-MMT@CS/G were well described by the Freundlich isotherm model and pseudo-second-order kinetic model. The maximum adsorption capacities were 2208.24 mg/g for MB, 1167.52 mg/g for MEB, and 806.31 mg/g for TCH. Electrostatic interactions, hydrogen bonding and van der Waals forces probably involved the adsorption process. As expected, this foam could exhibit better removal properties toward both charged and uncharged organic pollutants through the addition of H2O2 to trigger the Fenton degradation reaction. For non-adsorbable and uncharged bisphenol A (BPA), the removal efficiency was dramatically increased from 1.20 % to 92.77 % after Fenton degradation. Additionally, it presented outstanding recyclability. These results suggest that Fe-MMT@CS/G foam is a sustainable and efficient green material for the alleviation of water pollution.

Flexible fabrication chitosan-polyamidoamine aerogels by one-step method for efficient adsorption and separation of anionic dyes

Chitosan in situ grown polyamidoamine (CTS-Gx PAMAM (x = 0, 1, 2, 3)) aerogels were fabricated by a facile one-step freeze-drying method, with glutaraldehyde serving as a crosslinker. The three-dimensional skeletal structure of aerogel provided numerous adsorption sites and accelerated the effective mass transfer of pollutants. The adsorption kinetics and isotherm studies of the two anionic dyes were consistent with the pseudo-second-order and Langmuir models, indicating that the removal of rose bengal (RB) and sunset yellow (SY) was a monolayer chemisorption process. The maximum adsorption capacity of RB and SY reached 370.28 mg/g and 343.31 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacities of the two anionic dyes reached 81.10% and 84.06% of the initial adsorption capacities, respectively. The major mechanism between the aerogels and dyes was systematically investigated based on using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy analyses, confirming that electrostatic interaction, hydrogen bonding and van der Waals interactions were the main driving forces for the superior adsorption performance. Furthermore, the CTS-G2 PAMAM aerogel exhibited good filtration and separation performance. Overall, the novel aerogel adsorbent possesses excellent theoretical guidance and practical application potential for the purification of anionic dyes.

Stimuli-Responsive Ion Adsorbents for Sustainable Separation Applications

Stimuli-responsive ion absorbents (SRIAs) with reversible ion adsorption and desorption properties have recently attracted immense attention due to their outstanding functionalities for sustainable separation applications. Over the past decade, a series of SRIAs that respond to single or multiple external stimuli (e.g., pH, gas, temperature, light, magnetic, and voltage) have been reported to achieve excellent ion adsorption capacity and selectivity while simultaneously allowing for their reusability. In contrast to traditional adsorbents that are mainly regenerated through chemical additives, SRIAs allow for reduced chemical and even chemical-free regeneration capacities, thereby enabling environmentally friendly and energy-efficient separation technologies. In this review, we systematically summarize the materials and strategies reported to date for synthesizing single-, dual-, and multiresponsive ion adsorbents. Following a discourse on the fundamental mechanisms that govern their adsorption and desorption under various external stimuli, we provide a concise discussion of the regeneration capacity and application of these responsive ion adsorbents for sustainable water desalination, toxic ion removal, and valuable ion extract and recovery. Finally, we discuss the challenges in developing and deploying these promising multifunctional responsive ion adsorbents together with strategies to overcome these limitations and provide prospects for their future.

CO2 responsive self-standing Pickering emulsion gel stabilized with rosin-based surfactant modified cellulose nanofibrils

Emulsion gel was developed to provide desirable texture, palatability and functionality to food products. Tunable stability of emulsions is often desired, as in certain situations, the chemical content release usually relies on emulsion induced destabilization of the droplet. However, the destabilization for emulsion gel is difficult because of the formation of highly entangled networks. To address this issue, a fully biobased Pickering emulsion gel stabilized by cellulose nanofibrils (CNF) modified with a CO2 responsive rosin-based surfactant, maleopimaric acid glycidyl methacrylate ester 3-dimethylaminopropylamine imide (MPAGN) was reported. The emulsification/de-emulsification can be reversibly regulated because this surfactant has sensitive CO2 responsive property. MPAGN can be reversibly between active cationic (MPAGNH+) and inactive nonionic (MPAGN) responsive to CO2 and N2. The microstructure of the emulsion gel was observed and compared before and after the response. The rheological properties of emulsion gel stabilized by different concentrations of MPAGNH+ and different contents of CNF were studied separately. As 0.2 wt% CNF was dispersed in 1 mM MPAGNH+ solution, the obtained emulsion can be self-standing for long duration. The rheology study indicated that these emulsions show typical gel characteristics with shear-thinning behavior. The stabilization mechanism of these gel emulsion is a synergistic effect caused by the combination of CO2 responsive Pickering emulsion and intertwined network caused by the hydrogen-bond interaction among CNF.

Versatile CO2-responsive Sponges Decorated with ZIF-8 for Bidirectional Separation of Oil/Water and Controllable Removal of Dyes

The complex wastewater containing water-soluble dyes and water-insoluble oils has given rise to significant environmental concerns that demand urgent remediation. Herein, a novel "smart" multifunctional sponge (ZIF-8@PMS) stepwise decorated with ZIF-8 nanoparticles and CO2-responsive copolymer (poly(2-(diethylamino) ethyl methacrylate-co-3-(trimethoxysilyl)propyl acrylate-co-stearyl methacrylate) was successfully prepared for CO2 controllable oil/water separation and dyes removal. The results revealed that the sponge coated with CO2-responsive copolymer for three cycles (ZIF-8@PMS-3) exhibited optimal comprehensive properties. The ZIF-8@PMS-3 had excellent compressive-resilient characteristics and chemical stability. As expected, it displayed tunable wettability and charged state under the regulation of CO2. Based on these features, ZIF-8@PMS-3 presented highly efficient removal of oil and dyes, even for the dye-containing oil/water emulsions, via a synergistic combination of adsorption and separation methods. The adsorption capacity for oil and various organic solvents ranged from 21.3 to 50 g g-1. The maximum adsorption capacities toward anionic dyes: methyl orange with 1205.89 mg g-1 and methyl blue with 880.00 mg g-1 in the presence of CO2 through electrostatic interaction. In the absence of CO2, it achieved maximum adsorption capacities for cationic dyes, including malachite green with 1246.15 mg g-1 and rhodamine B with 203 mg g-1, primarily driven by π-π interactions. According to distinct adsorption mechanisms, ZIF-8@PMS-3 could selectively adsorb either anionic or cationic dyes by exploiting CO2 as a trigger. Furthermore, the separation efficiencies for both types of oil/water emulsions surpassed 99.9%, with respective fluxes of 1566.99 L m-2 h-1 (water-in-oil emulsion) and 310.37 L m-2 h-1 (oil-in-water emulsion). Additionally, the as-prepared sponges exhibited remarkable antibacterial properties and exceptional recyclability. Therefore, the ZIF-8@PMS-3 holds substantial promise for potential applications in practical industrial wastewater treatment.

CO2-responsive gels

CO₂-responsive materials undergo a change in chemical or physical properties in response to the introduction or removal of CO₂. The use of CO₂ as a stimulus is advantageous as it is abundant, benign, inexpensive, and it does not accumulate in a system. Many CO₂-responsive materials have already been explored including polymers, latexes, surfactants, and catalysts. As a sub-set of CO₂-responsive polymers, the study of CO₂-responsive gels (insoluble, cross-linked polymers) is a unique discipline due to the unique set of changes in the gels brought about by CO₂ such as swelling or a transformed morphology. In the past 15 years, CO₂-responsive gels and self-assembled gels have been investigated for a variety of emerging potential applications, reported in 90 peer-reviewed publications. The two most widely exploited properties include the control of flow (fluids) via CO₂-triggered aggregation and their capacity for reversible CO₂ absorption-desorption, leading to applications in Enhanced Oil Recovery (EOR) and CO₂ sequestration, respectively. In this paper, we review the preparation, properties, and applications of these CO₂-responsive gels, broadly classified by particle size as nanogels, microgels, aerogels, and macrogels. We have included a section on CO₂-induced self-assembled gels (including poly(ionic liquid) gels).

Preparation of Nanocellulose-Based Aerogel and Its Research Progress in Wastewater Treatment

Nowadays, the fast expansion of the economy and industry results in a considerable volume of wastewater being released, severely affecting water quality and the environment. It has a significant influence on the biological environment, both terrestrial and aquatic plant and animal life, and human health. Therefore, wastewater treatment is a global issue of great concern. Nanocellulose's hydrophilicity, easy surface modification, rich functional groups, and biocompatibility make it a candidate material for the preparation of aerogels. The third generation of aerogel is a nanocellulose-based aerogel. It has unique advantages such as a high specific surface area, a three-dimensional structure, is biodegradable, has a low density, has high porosity, and is renewable. It has the opportunity to replace traditional adsorbents (activated carbon, activated zeolite, etc.). This paper reviews the fabrication of nanocellulose-based aerogels. The preparation process is divided into four main steps: the preparation of nanocellulose, gelation of nanocellulose, solvent replacement of nanocellulose wet gel, and drying of nanocellulose wet aerogel. Furthermore, the research progress of the application of nanocellulose-based aerogels in the adsorption of dyes, heavy metal ions, antibiotics, organic solvents, and oil-water separation is reviewed. Finally, the development prospects and future challenges of nanocellulose-based aerogels are discussed.

Comparison between nanocellulose-polyethylenimine composites synthesis methods towards multiple water pollutants removal: A review

Nanocellulose/polyethylenimine composites have attracted growing attention due to their versatility as new materials for application in different fields. Water remediation is one of the traditional applications of these composites and their investigation as adsorbents for single water pollutants is well established. However, most water resources such as rivers, lakes, and even oceans contain complex mixtures of pollutants. Despite several recently published reviews on water purification technology, they only focused on these material as single pollutant removers and hardly mentioned their capacity to simultaneously recover multiple pollutants. Therefore, there is still a gap in the archived literature considering nanocellulose/polyethylenimine composites targeting water remediation with multiple water pollutants. In this review, methods for synthesizing such composites are classified and compared according to the mechanism of reactions, such as chemical crosslinking and physical adsorption, while outlining advantages and limitations. Then, the water pollutants mainly targeted by those composites are discussed in detail to expound the relationship between the synthesis method and the type and adsorption capacity. Finally, the last section presents challenges and opportunities of these nanocellulose/polyethylenimine composites as emerging sorbents for sustainable multiple water pollutants purification technologies. This review aims to lay out the basis for future developments of these composites for multiple water pollutants.

Cellulose/inorganic nanoparticles-based nano-biocomposite for abatement of water and wastewater pollutants

Nanostructured materials offer a significant role in wastewater treatment with diminished capital and operational expense, low dose, and pollutant selectivity. Specifically, the nanocomposites of cellulose with inorganic nanoparticles (NPs) have drawn a prodigious interest because of the extraordinary cellulose properties, high specific surface area, and pollutant selectivity of NPs. Integrating inorganic NPs with cellulose biopolymers for wastewater treatment is a promising advantage for inorganic NPs, such as colloidal stability, agglomeration prevention, and easy isolation of magnetic material after use. This article presents a comprehensive overview of water treatment approaches following wastewater remediation by green and environmentally friendly cellulose/inorganic nanoparticles-based bio-nanocomposites. The functionalization of cellulose, functionalization mechanism, and engineered hybrid materials were thoroughly discussed. Moreover, we also highlighted the purification of wastewater through the composites of cellulose/inorganic nanoparticles via adsorption, photocatalytic and antibacterial approach.

Facile Synthesis of ZIF-67 for the Adsorption of Methyl Green from Wastewater: Integrating Molecular Models and Experimental Evidence to Comprehend the Removal Mechanism

Organic dyes with enduring colors which are malodorous are a significant source of environmental deterioration due to their virulent effects on aquatic life and lethal carcinogenic effects on living organisms. In this study, the adsorption of methyl green (MG), a cationic dye, was achieved by using ZIF-67, which has been deemed an effective adsorbent for the removal of contaminants from wastewater. The characterization of ZIF-67 was done by FTIR, XRD, and SEM analysis. The adsorption mechanism and characteristics were investigated with the help of control batch experiments and theoretical studies. The systematical kinetic studies and isotherms were sanctioned with a pseudo-second-order model and a Langmuir model (R² = 0.9951), confirming the chemisorption and monolayer interaction process, respectively. The maximum removal capacities of ZIF-67 for MG was 96% at pH = 11 and T = 25 °C. DFT calculations were done to predict the active sites in MG by molecular electrostatic potential (MEP). Furthermore, both Molecular dynamics and Monte Carlo simulations were also used to study the adsorption mechanism.

Recent advances in biopolymer-based advanced oxidation processes for dye removal applications: A review

Over the past few years, synthetic dye-contaminated wastewater has attracted considerable global attention due to the low biodegradability and the ability of organic dyes to persist and remain toxic, causing numerous health and environmental concerns. As a result of the recalcitrant nature of those complex organic dyes, the remediation of wastewater using conventional wastewater treatment techniques is becoming increasingly challenging. In recent years, advanced oxidation processes (AOPs) have emerged as a potential alternative to treat organic dyestuffs discharged from industries. The most widely employed AOPs include photocatalysis, ozonation, Fenton oxidation, electrochemical oxidation, catalytic heterogeneous oxidation, and ultrasound irradiation. These processes involve the generation of highly reactive radicals to oxidize organic dyes into innocuous minerals. However, many conventional AOPs suffer from several setbacks, including the high cost, high consumption of reagents and substrates, self-agglomeration of catalysts, limited reusability, and the requirement of light, ultrasound, or electricity. Therefore, there has been significant interest in improving the performance of conventional AOPs using biopolymers and heterogeneous catalysts such as metal oxide nanoparticles (MONPs). Biopolymers have been widely considered in developing green, sustainable, eco-friendly, and low-cost AOP-based dye removal technologies. They inherit intriguing properties like biodegradability, renewability, nontoxicity, relative abundance, and sorption. In addition, the immobilization of catalysts on biopolymer supports has been proven to possess excellent catalytic activity and turnover numbers. The current review provides comprehensive coverage of different AOPs and how efficiently biopolymers, including cellulose, chitin, chitosan, alginate, gelatin, guar gum, keratin, silk fibroin, zein, albumin, lignin, and starch, have been integrated with heterogeneous AOPs in dye removal applications. This review also discusses the general degradation mechanisms of AOPs, applications of biopolymers in AOPs and the roles of biopolymers in AOPs-based dye removal processes. Furthermore, key challenges and future perspectives of biopolymer-based AOPs have also been highlighted.

Preparation of Bio-Based Aerogel and Its Adsorption Properties for Organic Dyes

The effective utilization of biomass and the purification of dye wastewater are urgent problems. In this study, a biomass aerogel (CaCO3@starch/polyacrylamide/TEMPO-oxidized nanocellulose, CaCO3@STA/PAM/TOCN) was prepared by combining nanocellulose with starch and introducing calcium carbonate nanoparticles, which exhibited a rich three-dimensional layered porous structure with a very light mass. Starch and nanocellulose can be grafted onto the molecular chain of acrylamide, while calcium carbonate nanopores can make the gel pore size uniform and have excellent swelling properties. Here, various factors affecting the adsorption behavior of this aerogel, such as pH, contact time, ambient temperature, and initial concentration, are investigated. From the kinetic data, it can be obtained that the adsorption process fits well with the pseudo-second-order. The Langmuir isotherm model can fit the equilibrium data well. The thermodynamic data also demonstrated the spontaneous and heat-absorbing properties of anionic and cationic dyes on CaCO3@STA/PAM/TOCN aerogels. The adsorption capacity of Congo red (CR) and methylene blue (MB) by CaCO3@STA/PAM/TOCN was 277.76 mg/g and 101.01 mg/g, respectively. Therefore, cellulose and starch-based aerogels can be considered promising adsorbents for the treatment of dye wastewater.

Preparation of adsorptive polyethyleneimine/polyvinyl chloride electrospun nanofiber membrane: Characterization and application

Landfilling and burning plastic waste, especially waste polyvinyl chloride (PVC), can produce highly toxic and carcinogenic by-products that threaten the ecosystem and human health. However, there is still a lack of proper methods for waste PVC recycling. Therefore, developing feasible ways for waste PVC recovery is urgently needed. The purpose of this study is to analyze the characteristics of PVC-based adsorptive nanofiber membranes and test their ability for the treatment of wastewater containing Cibacron Brilliant Yellow 3G-P, a widely used reactive dye. The polyethylenimine/polyvinyl chloride membrane (PEI/PVCM) was characterized by FTIR, FE-SEM, TGA, tensile analysis, water contact angle measurement, and zeta-potential analysis. The FTIR analysis confirmed that the PEI has successfully crosslinked with PVC. The FE-SEM images showed that the nanofibers constituting PEI/PVCM are compact with an average fiber diameter of 181 nm. The TGA results showed that the membrane was able to remain stable in wastewater below 150 °C. The average stress and strain of the PEI/PVCM were 7.64 ± 0.32 MPa and 934.14 ± 48.12%, respectively. The water contact angle and zeta potential analysis showed that after the introduction of PEI, the membrane converted from hydrophobic to hydrophilic, and the pH_pzc was increased from 3.1 to 1.08. The pure water flux of the membrane was measured at 0.1 MPa and the result was 3013 ± 60 L/m²‧h. The wastewater purification capability of PEI/PVCM was measured at an initial dye concentration of 10 ppm and pH 4-9 at 0.1 MPa. The reusability of PEI/PVCM was verified through three adsorption-desorption cycles. The results demonstrated that the PEI/PVCM is a reusable membrane for efficient purification of wastewater containing reactive dyes over a wide pH range (pH 4-8).

Lightweight and anisotropic cellulose nanofibril/rectorite composite sponges for efficient dye adsorption and selective separation

Constructing lightweight and porous adsorbents which can effectively remove dye contaminants is of great significance in the field of the sewage treatment. In this work, anisotropic cellulose nanofibril (CNF) composite sponges assisted by rectorites are fabricated through directional freeze-drying. The resulted composite sponge exhibits the superior saturated adsorption capacity and removal efficiency of 120.0 mg/g and 96.1% for methylene blue (MB), respectively, which is better than the pure CNF sponge and rectorite powders. This is attributed to the strong electrostatic interaction between CNFs and MB, and good cation exchange property of rectorites inside the three-dimensional (3D) highly porous composite sponge. The MB adsorption process of the composite sponge fits to the pseudo-second-order kinetic model and the Langmuir isotherm model well, which is affected by both boundary layer and intraparticle diffusion, resulting in a theoretical maximum adsorption capacity of 214.6 mg/g. Moreover, it also possesses a selective adsorption capacity for anionic and cationic dyes, which is expected to realize the separation treatment of different dyes according to actual application requirements.

CO2-responsive functional cotton fibers decorated with Ag nanoparticles for "smart" selective and enhanced dye adsorption

Novel Ag nanoparticles (NPs) decorated CO₂-responsive cotton fiber (PCCF@Ag) as eco-friendly adsorbent was prepared via in-situ growth of Ag NPs on the poly(2-(dimethylamino) ethyl methacrylate-co-4-acryloyloxybenzophenone) coated cotton fiber. The as-prepared PCCF@Ag displayed excellent adsorption performance toward both anionic and cationic dyes with or without CO₂ stimulation, even under a wide range of pH from 3 to 11. The maximum adsorption capacities of the as-prepared PCCF@Ag toward anionic dye (1538.5 mg g^-1 for MO) and cationic dyes (944.0 mg g^-1 for MEB and 415.6 mg g^-1 for NR) were satisfactory. The adsorption processes were described better by the Langmuir isotherm and pseudo-second-order kinetic models, respectively. Notably, upon CO₂ stimulation, the PCCF@Ag exhibited significantly enhanced adsorption capacity toward anionic dyes, following ultrafast adsorption rate, which made the PCCF@Ag could selectively adsorb anionic dyes from mixture because of greatly different adsorption rates between anionic dyes (adsorption equilibrium within 2 min) and cationic dyes (adsorption equilibrium over 12 h). Additionally, the PCCF@Ag could maintain over 91.0% of adsorption capacity even after ten cycles, indicating its outstanding reusability. Meanwhile, the as-obtained PCCF@Ag exhibited excellent antibacterial activity. Overall, the as-obtained PCCF@Ag could be considered as a promising dye scavenger for wastewater remediation.

Polydopamine-Modified Cellulose Nanofibril Composite Aerogel: An Effective Dye Adsorbent

In this study, a new cellulose nanofibril (CNF) composite aerogel was fabricated using a green and facile mussel-inspired coating strategy. First, the CNF hydrogel was crosslinked by calcium ion followed by immersion in dopamine solution. Second, the surface of CNF was modified using polydopamine (PDA) to obtain PDA@CNF (PCNF) composite aerogel. The PCNF composite aerogels had large surface areas (368.15 m²/g) and low bulk density (27.2 mg/cm³). The composite aerogel exhibited improved mechanical properties, which were almost three times compared with those of CNF aerogel. Moreover, PCNF composite aerogel had good resilience under a wet state. The PDA functional layer remarkably enhanced the adsorption capacities of the composite aerogel for methylene blue (MB). The maximum adsorption of MB was 208 mg/g at an initial dye concentration of 50 mg/L. The adsorption isotherm and kinetic behaviors of the composite aerogel were consistent with Langmuir and pseudo-second-order models. In addition, the PCNF composite aerogels had a high adsorption capacity over a wide pH range. The reuse experiment showed that the removal efficiency of the composite aerogel remained higher than 85% after five cycles. Therefore, PCNF composite aerogels may have potential application in wastewater treatment due to its environmental sustainability and low energy consumption.

Insights into efficient adsorption of the typical pharmaceutical pollutant with an amphiphilic cellulose aerogel

An amphiphilic cellulose aerogel (HCNC-TPB/TMC) was fabricated by grafting 1,3,5-Tris (4-aminophenyl)benzene (TPB) and trimesoyl chloride (TMC) onto the aldehyde nanocellulose through Schiff alkali and substitution reaction. The obtained HCNC-TPB/TMC exhibited good morphology with cellulose fiber and owned abundant hydrophilic amino and carboxyl groups and hydrophobic aromatic groups. The batch adsorption experiments demonstrated that HCNC-TPB/TMC showed excellent adsorption performance (Q_max = 526.32 mg g^-1) for sodium diclofenac (DCF), wide pH applicability (4-10) and outstanding stability and reusability. The DCF adsorption obeyed the pseudo-second-order kinetic model and the Langmuir isotherm, and underwent a spontaneous exothermic process. The main adsorption mechanisms involved electrostatic interaction, hydrogen bonds, π-π stacking interaction and hydrophobic effect. Importantly, the introduced carboxyl aromatic groups on TMC could effectively strengthen the hydrogen bonds and the π-π stacking between HCNC-TPB/TMC and DCF.

Lignocellulosic nanofibril aerogel via gas phase coagulation and diisocyanate modification for solvent absorption

Cellulose-based aerogels are considered to be carriers that can absorb oils and organic solvents owing to the merits of low density and high surface area. However, the natural hydrophility and poor mechanical strength often obstruct their widespread applications. In this work, Miscanthus-based dual cross-linked lignocellulosic nanofibril (LCNF) aerogels were prepared by gas phase coagulation and methylene diphenyl dissocyanate (MDI) modification. Due to physical and chemical cross-linking strategies, the optimally 4 M-LCNF aerogels had high surface area of 157.9 m²/g, water contact angle of 138.1°, and enhanced compression properties. Moreover, the modified aerogels exhibited absorption performance for various organic solvents, and the maximal absorption capacity of chloroform was 42 g/g aerogel. Because LCNF was directly produced from Miscanthus without using bleaching reagents, this research provided a more sustainable methodology to utilize lignocelluloses to design robust aerogels to deal with the leakage of oil and organic solvents in industrial applications.

Development of a metal-free black phosphorus/graphitic carbon nitride heterostructure for visible-light-driven degradation of indomethacin

The development of affordable and efficient technologies for the removal of pharmaceuticals and personal care products (PPCPs) from water has recently been the subject of extensive attention. In this study, a black phosphorus/graphitic carbon nitride (BP-g-C₃N₄) heterostructure is fabricated as an extremely active metal-free photocatalyst via a newly-developed exfoliation strategy. The BP-g-C₃N₄ shows an 11 times better decomposition rate of a representative PPCPs-type pollutant, indomethacin (IDM), compared to the widely-used P25 TiO₂ under real-sunlight illumination. Also, its visible-light activity is even better than that of the best photocatalysts previously developed, but only consumes 1/10-1/4 of the catalyst. The results show that BP performs a cocatalyst-like behavior to catalyze the generation of reactive oxygen species, thus speeding up the decomposition of IDM. In addition, the BP-g-C₃N₄ photocatalyst also exhibits excellent IDM removal efficiency in authentic water matrices (tap water, surface water, and secondarily treated sewage effluent). Large-scale application demonstration under natural sunlight further reveals the practicality of BP-g-C₃N₄ for real-world water treatment operations. Our work will open up new possibilities in the development of purely metal-free photocatalysts for "green" environmental remediation applications.

Removal of methylene blue from wastewater using ternary nanocomposite aerogel systems: Carboxymethyl cellulose grafted by polyacrylic acid and decorated with graphene oxide

In this study, environmentally-friendly nanocomposite hydrogels were fabricated. These hydrogels consisted of semi-interpenetrating networks of carboxymethyl cellulose (CMC) molecules grafted to polyacrylic acid (PAA), as an eco-friendly and non-toxic polymer with numerous carboxyl and hydroxyl functional groups, which were reinforced with different levels of graphene oxide particles (0.5, 1.5 or 3% wt). Field-emission electron scanning microscopy (FESEM) images indicated that the pore size of the nanocomposites decreased with increasing graphic oxide concentration. The presence of the graphic oxide increased the storage modulus and thermal stability of the nanocomposite hydrogels. The hydrogels had an adsorption capacity of 138 mg/g of a model cationic dye pollutant (methylene blue) after 250 min. Moreover, a reusability test showed that the adsorption capacity remained at around 90% after 9 cycles. Density functional theory (DFT) simulations suggested that the adsorption of methylene blue was mainly a result of π-π bonds, hydrogen bonds, and electrostatic interactions with graphene oxide. Our results indicated that the nanocomposite hydrogels fabricated in this study may be eco-friendly, stable, efficient, and reusable adsorbents for ionic pollutants in wastewater treatment.

Multiple chemical modifications and Cd2+ adsorption characteristics of sludge-based activated carbon

The multiple chemical modifications were carried out to achieve N-doping and pore-making to modify sludge-based activated carbon (SACU–PF′). SACU–PF′ possessed abundant functional groups and high adsorption capacity of Cd2+.

Water treatment using stimuli-responsive polymers

Stimuli-responsive polymers are a new category of smart materials used in water treatment via a stimuli-induced purification process and subsequent regeneration processes.

Giving Penetrable Remote-Control Ability to Thermoresponsive Fibrous Composite Actuator with Fast Response Induced by Alternative Magnetic Field

An alternative magnetic field (AMF)-induced electrospun fibrous thermoresponsive composite actuator showing penetrable remote-control ability with fast response is shown here for the first time. The built-in heater of magnetothermal Fe₃O₄ nanoparticles in the actuator and the porous structure of the fibrous layer contribute to a fast actuation with a curvature of 0.4 mm⁻¹ in 2 s. The higher loading amount of the Fe₃O₄ nanoparticles and higher magnetic field strength result in a faster actuation. Interestingly, the composite actuator showed a similar actuation even when it was covered by a piece of Polytetrafluoroethylene (PTFE) film, which shows a penetrable remote-control ability.

Mechanistically understanding adsorption of methyl orange, indigo carmine, and methylene blue onto ionic/nonionic polystyrene adsorbents

The involved interaction information concerning adsorbate-adsorbate and adsorbate-adsorbent is indispensable for developing and optimizing adsorption treatment of dye wastewater. Single and bi-solute adsorption of methyl orange (MO), indigo carmine (IC), and methylene blue (MB) on polystyrene anion exchanger (PsAX), defunctionalized version of PsAX (DF-PsAX), and hyper-cross-linked polystyrene adsorbent (MN200) were investigated to obtain a mechanistic understanding. Under acidic condition, higher adsorption efficiencies of PsAX due to extra intermolecular interactions of MO between the protonated tertiary amine group and the sulfate groups were observed, while strong alkaline condition is favorable for the adsorption of IC and MB by PsAX. MN200 exhibited much larger adsorption capacity toward MB than that toward MO or IC, because the fused-rings structure of MB is more polarizable and can form stronger nonionic intermolecular attractions with the matrix structure of polystyrene adsorbents. Bi-solute adsorption reveals that MO has obvious competitive effect toward IC adsorption at low concentrations, but it is not the case for the adsorption at high concentrations, where IC molecules can form intermolecular H-bonding interactions to defend the competition. the thermodynamic parameters confirm the endothermic and spontaneous nature of MO adsorption by PsAX, and ≈ 48 KJ mol^-1 of the enthalpy change (∆H) imply the adsorption is not just physical absorption. Additionally, water/ethanol mixture solution of NaCl can almost thoroughly regenerate the exhausted PsAX, whereas only aqueous solution without ethanol is invalid.

Cellulose-Based Hydrogels and Aerogels Embedded with Silver Nanoparticles: Preparation and Characterization

The paper presents the preparation and characterization of novel composite materials based on microcrystalline cellulose (MCC) with silver nanoparticles (Ag NPs) in powder and gel forms. We use a promising synthetic conception to form the novel composite biomaterials. At first MCC was modified with colloidal solution of Ag NPs in isopropyl alcohol prepared via metal vapor synthesis. Then Ag-containing MCC powder was used as precursor for further preparation of the gels. The hydrogels were prepared by dissolving pristine MCC and MCC-based composite at low temperatures in aqueous alkali solution and gelation at elevated temperature. To prepare aerogels the drying in supercritical carbon dioxide was implemented. The as-prepared cellulose composites were characterized in terms of morphology, structure, and phase composition. Since many functional properties, including biological activity, in metal-composites are determined by the nature of the metal-to-polymer matrix interaction, the electronic state of the metal was carefully studied. The studied cellulose-based materials containing biologically active Ag NPs may be of interest for use as wound healing or water-purification materials.

Study on the adsorption properties of methyl orange by natural one-dimensional nano-mineral materials with different structures

Methyl orange (MO) is a common anionic azo dye that is harmful to the environment and biology, so it must be treated innocuously before it can be discharged. Adsorption is an effective method to remove anionic dyes. Nanotube mineral is a natural one-dimensional adsorption material, and its unique morphology and structure endow it with good adsorption capacity. Although there are many related studies, there is a lack of in-depth discussions on the influence of nanotube's composition and structure on the adsorption of dyes and other pollutants. In this paper, two kinds of natural one-dimensional silicate minerals [halloysite nanotubes (HNTs) and chrysotile nanotubes (ChNTs)] with similar morphology but slightly different compositions and crystal structures were used as adsorbents, and MO solution was used as simulate pollutants. It is the first time to discuss in depth the influence of the composition and structure of nanotube minerals on their charge properties and the adsorption performance of methyl orange dyes. It is found that HNTs and ChNTs have different adsorption capacity due to the difference of electronegativity between Al³⁺ and Mg²⁺ in the crystal, so they possess negative and positive charges respectively in near-neutral solution, which leads to the adsorption capacity of MO by ChNTs with positive charges which is greater than that of HNTs.

Facile and Scalable Fabrication of Antibacterial CO2-Responsive Cotton for Ultrafast and Controllable Removal of Anionic Dyes

A novel CO₂-responsive cotton as an eco-friendly adsorbent derived from poly(4-acryloyloxybenzophenone-co-2-(dimethylamino) ethyl methacrylate) and cotton was fabricated via a facile and fast dip-coating method. As expected, upon CO₂ stimulation, the protonated cotton presented CO₂-induced "on-off" selective adsorption behaviors toward anionic dyes owing to electrostatic interactions. The adsorption isotherms and kinetics of the CO₂-responsive cotton toward anionic dyes obeyed the Langmuir isotherm and pseudo-second-order kinetics models, respectively. It is noteworthy that the CO₂-responsive cotton exhibited high adsorption capacity and ultrafast adsorption rate toward anionic dyes with the maximum adsorption capacities of 1785.71 mg g^-1 for methyl orange (MO), 1108.65 mg g^-1 for methyl blue (MB), and 1315.79 mg g^-1 for naphthol green B (NGB), following the adsorption equilibrium times of 5 min for MO, 3 min for MB, and 4 min for NGB. Moreover, the CO₂-responsive cotton also exhibited high removal efficiency toward anionic dyes in synthetic dye effluent. Additionally, the CO₂-responsive cotton could be facilely regenerated via heat treatment under mild conditions and presented stable adsorption properties even after 15 cycles. Finally, the as-prepared CO₂-responsive cotton exhibited outstanding antibacterial activity against E. coli and S. aureus. In summary, this novel CO₂-responsive cotton can be viewed as a promising eco-friendly adsorbent material for potential scalable application in dye-contaminated wastewater remediation.