Temperature and pH responsive cellulose filament/poly (NIPAM-co-AAc) hybrids as novel adsorbent towards Pb(II) removal

Preparation of graphene based composites using silane and Pyracantha fortuneana and their application in Metformin adsorption from aqueous solution

Metformin, a typical pharmaceutical and personal care product (PPCPs), has a significant role in protecting brain cognitive function and delaying multiple organs aging, as well as causes seriously endocrine and reproductive interference to aquatic organisms due to drug abuse. Graphene that is of stable structure, flexible connection between carbon atoms, and the conjugated large pi bonds has been used to wastewater treatment, while Graphene-based materials used to remove PPCPs are rarely reported. Therefore, two graphene oxide (GO) based materials, including silane coupling agent modified product (CTOS-mGO) and Pyracantha fortuneana proanthocyanidin extract reduced product (PFPA-rGO), were used for metformin removal from aqueous solution as well as revealed the mechanism in this adsorption process. The results showed that metformin could be quickly and effectively removed by GO, CTOS-mGO and PFPA-rGO, of which the best material of adsorption effects was CTOS-mGO. The pseudo-second-order kinetic could effectively describe their adsorption process, and they achieved more than 80% removal rate within 15 to 20 min. Metformin adsorption by GO, CTOS-mGO and PFPA-rGO were all spontaneous and exothermic. CTOS-mGO was of the largest adsorption capacity and recycling utilization for metformin removal in comparison with GO and PFPA-rGO. The optimal adsorption temperature and pH for the GO and CTOS-mGO, PFPA-rGO adsorbents were 293 K and pH 6.0, 293 K and pH 7.0, 303 K and pH 6.0, respectively. Our results suggested that the aromatic rings and the abundant oxygen-containing functional groups distributed on the surface of the sheets endowed them with the characteristics of π-electron acceptors or donors, and metformin with dissociative properties could serve as a stabilizer for this π-π interaction. In addition, the electrostatic interaction between the positively charged metformin and the negatively charged GO and CTOS-mGO were also important contributors to the adsorption reaction. Our results emphasized that the GO based materials might be an effective method for alleviating metformin and other PPCPs pollution, which also provided a reference for environmental remediation of similar pollutants.

Responsive nanocellulose-PNIPAM millicapsules

HYPOTHESIS

Milli- and micro-capsules are developed to facilitate the controlled release of diverse active ingredients by passive diffusion or a triggered burst. As applications expand, capsules are required to be increasingly multi-functional, combining benefits like encapsulation, response, release, and even movement. Balancing the increasingly complex demands of capsules is a desire to minimize material usage, requiring efficient structural and chemical design. Designing multifunctional capsules with complex deformation should be possible even after minimizing the material usage through use of sparse fiber networks if the fibers are coated with responsive polymers.

EXPERIMENTS

Here capsules are created with a shell made from a mesh of nanoscale bacterial cellulose fibers that provide mechanical strength at very low mass levels, while a coating of thermoresponsive Poly(N-isopropylacrylamide), PNIPAM, on the fibers provides control of permeability, elastic response, and temperature response. These properties are varied by grafting different amounts of polymer using particular reaction conditions.

FINDINGS

The addition of PNIPAM to the cellulose mesh capsule enhances its mechanical properties, enabling it to undergo large deformations and recover once stress is removed. The increased elastic response of the capsule also provides reinforcement against drying-induced capillary stresses, limiting the degree of shrinkage during dehydration. Time-lapse microscopy demonstrates thermoreversible swelling of the capsules in response to temperature change. Cycles of swelling and shrinkage drive solvent convection to and from the capsule interior, allowing exchange of contents and mixing with the bulk fluid on a time scale of seconds. Because the cellulose capsules are produced via emulsion-templated fermentation, the polymer-modified biocapsule concept introduced here presents a pathway toward the sustainable and scalable manufacture of multifunctional responsive capsules.

A critical review on the removal of lead (heavy metal) by using various adsorbents from aqueous solution

One of the biggest problems globally is the presence of lead in water resources. Due to increased Industrialization, the presence of the heavy metal lead in the environment is a severe worry. Excessive lead poisoning harms all the aquatic systems, which poses a concern for human health and damages this ecosystem through eutrophication. Various techniques are used to collect and remove lead from wastewater to protect aquatic bodies. Adsorption is among the finest methods for eliminating lead from wastewater since it is easy to use, effective, universal, inexpensive, and environmentally friendly. Adsorption is one of the most efficient and effective techniques employed even at low temperatures, as we will explore in this paper. The removal of lead (heavy metal) by adsorption utilizing various adsorbents, including cellulose, industrial by-products, forest wastes, and biotechnology wastes, was evaluated in this paper at various levels from the numerous research and literature. Then, various adsorbent types were assessed in terms of removal efficiency, adsorption capacity, temperature, optimal pH, sorbent dose, and contact time. The paper also examines or researches adsorbent concentration, critical studies, and lead removal percentage. The growth of low-cost adsorbents offers challenges for lead recovery and removal in the near and far future.

Nanocellulose-based membranes with pH- and temperature-responsive pore size for selective separation

Smart gating membranes have drawn much attention due to the controllable pore structure. Herein, a smart gating membrane with dual responsiveness was prepared from bacteria cellulose (BC) grafted with pH- and temperature-responsive polymers. By external stimulation, the average pore size of the membrane can be controlled from 33.75 nm to 144.81 nm, and the pure water flux can be regulated from 342 to 2118 L·m-2·h-1 with remarkable variation in the pH range of 1-11 and temperature range of 20-60 °C. The adjustability of pore size is able to achieve the gradient selective separation of particles and polymers with different sizes. In addition, owing to the underwater superoleophobicity and the nanoscale pore structure, the membrane separation efficiencies of emulsified oils are higher than 99 %. Moreover, the controllable pore size endows the membrane with good self-cleaning performance. This nanocellulose-based smart gating membrane has potential applications in the fields of controllable permeation, selective separation, fluid transport, and drug/chemical controlled release systems.

Comprehensive review on pH and temperature-responsive polymeric adsorbents: Mechanisms, equilibrium, kinetics, and thermodynamics of adsorption processes for heavy metals and organic dyes

Wastewater treatment technologies have been developed to address the health and environmental risks associated with toxic and cancer-causing dyes and heavy metals found in industrial waste. The most commonly used method to mitigate and treat such effluents is adsorption, which is favored for its high efficiency, low costs, and ease of operation. However, traditional adsorbents have limitations in terms of regeneration and selectivity compared to smart adsorbents. Smart polymeric adsorbents, on the other hand, can undergo physical and chemical changes in response to external factors like temperature and pH, enabling a selective adsorption process. These adsorbents can be easily regenerated and reused with minimal generation of secondary pollutants during desorption. The unique properties acquired by stimuli-responsive adsorbents have encouraged researchers to investigate their potential for the selective and efficient removal of organic dyes and heavy metals. This comprehensive review focuses on two common stimuli, pH and temperature, discussing the fabrication methods and characteristics of smart adsorbents responsive to these factors. It also provides an overview of the mechanisms, isotherms, kinetics, and thermodynamics of the adsorption process for each type of stimuli-responsive adsorbent. Finally, the review concludes with discussions on future perspectives and considerations.

Synthesis of GG-g-P(NIPAM-co-AA)/GO and evaluation of adsorption activity for the diclofenac and metformin

The grafting of biopolymer gum ghatti (GG) over the PNIPAM and PAA was done and loaded with graphene oxide (GO). Aim of this work is carried out combine adsorption of sodium diclofenac (SD) and metformin (MF) by the prepared hydrogels under influence of various parameters. The adsorbent GG-g-P(NIPAM-co-PAA)/GO(3 mg) chosen for adsorption activity as it displayed highest swelling capacity. The effect of amount of both adsorbents GG-g-P(NIPAM-co-PAA and GG-g-P(NIPAM-co-PAA)/GO(3 mg) showed that highest adsorption capacity found at 40 mg of adsorbents for both drugs at conditions: 100 mg/L concentration, 30 °C, 24 h and pH 6 and subsequently became stable. Both the drugs were removed in greater amount at 25 mg/L concentration, 24 h of contact time, 30 °C, 40 mg amount of both adsorbents and pH 6. Effect of time revealed that as time elevated from 2 h to 12 (100 mg/L concentration,, 30 °C, 40 mg amount of both adsorbents and pH 6) led to increase adsorption efficiency and after that increase time did not much impact on adsorption activity. Adsorption activity of hydrogels declined with increase of temperature (100 mg/L concentration, 12 h, 40 mg amount of both adsorbents and pH 6). The acidic conditions favored adsorption of SD while MF adsorbed under the weak acidic(100 mg/L concentration, 30 °C, 12 h, 40 mg amount of both adsorbents). However, basic conditions did not much influence on adsorption of MF but effected on adsorption activity of SD. Adsorption isotherm and kinetic model suggested that adsorption is homogenous and chemical in nature. The maximum adsorption capacity (qm) found to be 289.01 and 154.55 mg/g for SD and MF respectively.

Graphical abstract

Supplementary information

The online version contains supplementary material available at 10.1007/s40201-023-00867-w.

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.

Temperature-Sensitive Fragrance Microcapsules with Double Capsule Walls: A Study on Preparation and Sustained Release Mechanism

Microcapsules are small particles that can effectively protect a core material from degradation. Microcapsules with double capsule walls can improve stability and reduce breakage due to the fact that the physical and chemical properties of double-walled materials can complement each other, thus enhancing the quality and applicability of a microcapsule. Microcapsules can achieve controlled release of core materials by using a temperature-sensitive wall material. In this research, gelatin was used as the inner wall material for these double-walled microcapsules. The outer wall material was a composite material prepared by the reaction of a hydroxyl group in gum arabic with an amino group in N-isopropylacrylamide (NIPAM) in the presence of N, N'-methylene bisacrylamide (BIS), while lavender fragrance oil served as the core material. A complex coalescence method was used for the preparation of microcapsules with double capsule walls. The effects of different proportions of gum arabic to NIPAM on the core loading, microcapsule yield and thermal stability of microcapsules were studied in detail. Additionally, the stability of these fragrance microcapsules with double capsule walls in different solvents and pH values was evaluated. The sustained release properties and mechanism of cotton fabrics treated with prepared fragrance microcapsules were investigated. The results show that the microcapsules prepared with a 10:1 ratio of NIPAM to gum arabic have good temperature responsiveness. Therefore, clothing treated with microcapsules with temperature-sensitive wall materials can ensure that the human body has a fresh and pleasant smell in the case of perspiring in summer.

A smart gating nanocellulose membrane showing selective separation and self-cleaning performance

A smart gating membrane based on thermal-sensitive poly (N-isopropyl acrylamide) (PNIPAM)-grafted nanocellulose and carbon nanotube (CNT) was prepared. The presence of PNIPAM shell on cellulose nanofibrils (CNFs) endow the composite membrane with thermal responsiveness. By external stimulation, an increase temperature from 10 °C to 70 °C allows the average pore size of the membrane to be controlled from 28 nm to 110 nm, as well as the water permeance from 440 L·m^-2·h^-1·bar^-1 to 1088 L·m^-2·h^-1·bar^-1. The gating ratio of the membrane can reach 2.47. The photothermal effect of CNT rapidly warms up the membrane to the lowest critical solution temperature in the water, avoiding the constraint that the whole water phase cannot be heated throughout the practical use process. The membrane can precisely control the nanoparticles to concentrate at 25.3 nm, 47.7 nm or 102 nm by adjust the temperature. In addition, the water permeance can be restored to 370 L·m^-2·h^-1·bar^-1 by washing the membrane under light. The smart gating membrane has a wide application in substance multi-stage separation and selective separation, and it can realize self-cleaning.

Facile fabrication of a broad-spectrum starch/poly(α-l-lysine) hydrogel adsorbent with thermal/pH-sensitive IPN structure through simultaneous dual-click strategy

A thermal/pH-sensitive interpenetrating network (IPN) hydrogel was prepared facilely from starch and poly(α-l-lysine) through amino-anhydride and azide-alkyne double-click reactions in one pot. The synthesized polymers and hydrogels were systematically characterized using different analytical techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and rheometer. The preparation conditions of the IPN hydrogel were optimized via one-factor experiments. Experimental results indicated the IPN hydrogel possessed pH and temperature sensitivity. Effect of different parameters (pH, contact time, adsorbent dosage, initial concentration, ionic strength, and temperature) on adsorption behavior were investigated in monocomponent system with cationic methylene blue (MB) and anionic Eosin Y (EY) as model pollutants. The results indicated that the adsorption process of the IPN hydrogel for MB and EY followed pseudo-second-order kinetics. The adsorption data for MB and EY fitted well with the Langmuir isotherm model, indicating monolayer chemisorption. The good adsorption performance was due to various active functional groups (-COOH, -OH, -NH₂, etc.) in the IPN hydrogel. The strategy described here opens up a new way for preparing IPN hydrogel. The as-prepared hydrogel exhibits potential application and bright prospects as an adsorbent in wastewater treatment.

Liquid Foam Stabilized by a CO2-Responsive Surfactant and Similarly Charged Cellulose Nanofibers for Reversibly Plugging in Porous Media

CO₂ foams are of great importance in oil recovery but challenging in some aspects like long-term stabilization and time-separated conflict. In this work, a stability-enhanced switchable foam was fabricated using bis-(2-hydroxyethoxy) olefine amine (BOA) and trace amounts (0.05 wt %) of cationic-modified cellulose nanofibers (CCNFs). The CCNF was developed using sequentially functionalized CNF with diamine groups, which were essential to promote the aqueous dispersibility and a key for strengthening the stabilization of foam. The combination of similarly charged CCNFs and BOA in the presence of CO₂ contributed to both surface activity and viscoelasticity. It was demonstrated that CCNFs were entangled and stacked to form the compact films and possessed the ability to costabilize the lamellae, as observed by microscopic studies. In addition, the intermolecular H-bonds were promoted in the binary system after being protonated by CO₂ and thus balancing the electrostatic forces, as explored by spectroscopy characterizations. The soft fibrous structure of the CCNF was also capable of wrapping gas bubbles in the form of a functional membrane with both low gas permeability and high surface potential, which slowed down the coarsening and coalescence. Of particular interest is that the reversible protonation state of CCNF-BOA complexes upon the alternate treatment with CO₂/N₂ led to reversible fast foaming/defoaming, which would be beneficial to construct the steerable plugging in the sand pack. This work is expected to provide a new direction and application of the CO₂ responsive foam stabilized by similarly charged nanocellulose fibers in oilfield development.

Synthesis and Characterization of Thermosensitive P(NIPAAm-co-AAc)-Grafted Silica Nanocomposites for Smart Architectural Coatings

In this study, a new class of thermosensitive poly(N-isopropylacrylamide)-co-poly(acrylic acid) (P(NIPAAm-co-AAc))-grafted modified silica (m-silica) nanocomposites was prepared using a sol-gel technique. The addition of silica to P(NIPAAm-co-AAc) copolymer hydrogel has the potential to open up new applications in the development of thermosensitive building materials by leveraging the favorable thermal characteristics of P(NIPAAm-co-AAc). The silica was prepared using 3-aminopropyltriethoxysilane and 4,4'-azobis(4-cyanovaleric acid) to form the m-silica powder, which increased the adhesion between the organic and inorganic hybrid materials. The P(NIPAAm-co-AAc) copolymer hydrogel was mixed with the m-silica to form the P(NIPAAm-co-AAc)-grafted m-silica nanocomposites. Scanning electron microscopy, X-ray diffraction analysis, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and thermosensitive measurement were conducted to evaluate the structure and water-holding capacity of the nanocomposites. The results indicated that the P(NIPAAm-co-AAc)-grafted m-silica nanocomposites could retain water for more than 300 min at temperatures higher than the lower critical solution temperature. The P(NIPAAm-co-AAc)-grafted m-silica nanocomposites exhibited favorable thermosensitive properties and may therefore be applied in smart architectural coatings.

Facile auto-combustion synthesis of calcium aluminate nanoparticles for efficient removal of Ni(II) and As(III) ions from wastewater

We herein report the synthesis of monoclinic calcium aluminate (CaAl₂O₄) nanoparticles via a facile auto-combustion method followed by calcination. We performed the auto-combustion method using aluminium nitrate and calcium nitrate as oxidants and different fuels as reductants such as urea, glycine, and a mixture of urea and glycine, with various fuel-to-oxidant equivalence ratios (Φc). Then, the combusted samples were calcined at different temperatures; 600 and 800 °C. The products were characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, field-emission scanning electron microscope, and high-resolution transmission electron microscope. CaAl₂O₄ nanoparticles with an average crystallite size of 40.4, 38.8, and 33.7 nm were obtained after calcination at 800 °C using the aforementioned fuels, respectively. TEM images revealed that CaAl₂O₄ nanoparticles tend to form partially sintered aggregates owing to the high thermal treatment temperature, so they have non-uniform shapes. The produced CaAl₂O₄ nanoparticles exhibited good absorptivity toward Ni(II) and As(III) ions form aqueous media. The maximum sorption capacities (q_m) of CaAl₂O₄ for the removal of Ni(II) and As(III) were found to be 58.73 and 43.9 mg.g^-1, at pH 7 and 5, respectively. The equilibrium isotherms and adsorption kinetics studies revealed that the adsorption data fitted well Freundlich isotherm and pseudo-second-order models, respectively. Besides, the adsorption of Ni(II) and As(III) ions on CaAl₂O₄ nanoparticles is physisorption. Overall, the obtained results indicated that calcium aluminate nano-adsorbent is a good candidate for the removal of Ni(II) and As(III) ions from wastewater, due to its high efficiency, stability, and re-usability.

Novel Thermosensitive-co-Zwitterionic Sulfobetaine Gels for Metal Ion Removal: Synthesis and Characterization

Zwitterionic betaine polymers are promising adsorbents for the removal of heavy metal ions from industrial effluents. Although the presence of both negative and positively charged groups imparts them the ability to simultaneously remove cations and anions, intra- and/or inter-chain interactions can significantly reduce their adsorption efficiencies. Therefore, in this study, novel gels based on crosslinked co-polymers of thermosensitive N-isopropylacrylamide (NIPAAM) and zwitterionic sulfobetaine N,N-dimethylacrylamido propyl ammonium propane sulfonate (DMAAPS) were synthesized, characterized, and evaluated for ion removal. Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) analyses confirmed the success of the co-polymerization of NIPAAM and DMAAPS to form poly(NIPAAM-co-DMAAPS). The phase transition temperature of the co-polymer increased with increasing DMAAPS content in the co-polymer, indicating temperature-dependent amphiphilic behavior, as evidenced by contact angle measurements. The ion adsorption analyses of the poly(NIPAAM-co-DMAAPS) gels indicated that co-polymerization increased the molecular distance and weakened the interaction between the DMAAPS-charged groups (SO3- and N+), thereby increasing the ion adsorption. The results confirmed that, with a low concentration of DMAAPS in the co-polymer gels (~10%), the maximum amount of Cr3+ ions adsorbed onto the gel was ~58.49% of the sulfonate content in the gel.

Methacrylated alkali lignin grafted P(Nipam-Co-AAc) copolymeric hydrogels: Tuning the mechanical and stimuli-responsive properties

The current study reports the preparation of lignin grafted temperature and pH responsive hydrogels through copolymerization of N-isopropylacrylamide, acrylic acid and varying amount of lignin methacrylate (LMA = 50, 100, 150 and 200 mg) as crosslinker adopting radical polymerization technique. Functional group and structural characterizations were carried out to confirm hydrogels synthesis and their network structure. The variation in pore size on addition of lignin revealed the tuning of pores as well as swelling capacity of the hydrogels by suitable amount of LMA. All LMA grafted hydrogels showed temperature responsive behavior and pH dependent sensitivity in swelling, with reduced equilibrium swelling capacity values compared to sample without lignin. In alkali medium at room temperature, the maximum swelling capacity with 48% higher retention was noticed, while a significant reduction in swelling was observed at 40 °C in all media. The addition of lignin still preserved the tensile strength up to 100 kPa and compressive load bearing ability up to 30 kPa in freeze dried state with adequate interfacial stress transfer. An increase in lignin concentration showed enhanced storage modulus (~two-fold increase), adequate loss modulus values and improved cell viability, which paves the way for possible biomedical applications.

Facile Preparation and Dye Adsorption Performance of Poly(N-isopropylacrylamide-co-acrylic acid)/Molybdenum Disulfide Composite Hydrogels

Using N-isopropylacrylamide (NIPAM) and acrylic acid (AAc) as monomers, N,N'-methylenebisacrylamide (MBA) as a cross-linking agent, and molybdenum disulfide (MoS2) as functional particles, a P(NIPAM-co-AAc)/MoS2 composite hydrogel was prepared by free radical polymerization initiated by ultraviolet light. The results of Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy show that MoS2 has been successfully introduced into the P(NIPAM-co-AAc) system, and the obtained composite hydrogel has a porous network structure. Studies on the swelling property and dye adsorption performance show that the addition of MoS2 can increase the swelling ratio of P(NIPAM-co-AAc) hydrogels to a certain extent and can significantly improve the ability of the P(NIPAM-co-AAc) hydrogel to adsorb methylene blue (MB). The adsorption process of MB by the composite hydrogels conforms to the pseudo-second-order kinetics and the Langmuir isotherm adsorption models. The estimated equilibrium adsorption capacity (Q m) using the Langmuir isotherm model can reach 1258 mg/g, mainly due to the electrostatic interaction between the negatively charged groups -COO- and MoS2 particles on the network structure and the positively charged dye MB. The adsorption of MB by P(NIPAM-co-AAc)/MoS2 composite hydrogels depends on the temperature during adsorption. Compared with room temperature, a high temperature of 40 °C above the poly(N-isopropylacrylamide) (PNIPAM) phase transition temperature (∼32 °C) leads to a decreased adsorption capacity of the P(NIPAM-co-AAc)/MoS2 composite hydrogel for MB due to the enhanced hydrophobic properties of the network structure and the decrease of the swelling ratio. The prepared hydrogel material can be used as a good adsorbent for dyes, which is promising in wastewater treatment.

The removal of Cu(II) and Pb(II) ions from aqueous solutions by temperature-sensitive hydrogels based on N-isopropylacrylamide and itaconic acid

This study deals with the potential use of poly(N-isopropylacrylamide-co-itaconic acid) temperature-sensitive hydrogels as an adsorbent for the removal of Cu(II) and Pb(II) ions from aqueous solutions. For this aim, the adsorption properties of hydrogels were examined by adsorption capacities, adsorption isotherm, and adsorption kinetics experiments. To describe the adsorption characteristics of hydrogels, the obtained experimental data were evaluated by Langmuir, Freundlich, Redlich-Peterson, and Dubinin-Radushkevich isotherm models. Adsorption kinetics experiments were carried out not only in single systems but also in binary systems where both ions were at equal initial concentrations for competitive adsorption studies. To predict the behaviors of the competitive and non-competitive adsorption process of ions onto hydrogels, the experimental adsorption data were analyzed by the pseudo-first-order model and the pseudo-second-order model. According to non-competitive ion removal findings, the adsorption capacities followed order Cu(II) > Pb(II) for all hydrogels, and the pseudo-second-order kinetic model explained the adsorption properties of the hydrogels. Competitive ion removal studies showed that all hydrogels were selective to Cu(II) ion. Furthermore, in the case of comparative investigations both of competitive Cu(II) and competitive Pb(II) removal by hydrogels, the metal ion removal capacity of N10 hydrogel was found as a bit higher than that of N7.5 and N5 in 48 h. That is, as the acidic group content increased in the hydrogel network, the adsorption capacity values also increased. In addition, the reusability of temperature-sensitive hydrogels seems possible without regeneration or after regenerating with acid, in case the temperature is increased above the LCST. Furthermore, even if it cannot be reused, these hydrogels that retain metal ions reach very small volumes by shrinking when the LSCT is exceeded, and thus they can be eliminated more easily than other conventional gels due to their small size. As a result, this temperature-sensitive hydrogel may propose as an alternative environmentally friendly adsorbent candidate for can be used for water purification and wastewater treatment.

Recent studies on cellulose-based fluorescent smart materials and their applications: A comprehensive review

The progress of bio-based fluorescent smart materials and their multifunctional applications have attained increasing interest in the recent decades. Cellulose is among the cheapest and widespread raw material on earth which can be modified into diverse useful materials. This review summarizes the chemical modification of cellulose into smart fluorescent materials. This further highlights on the fabrication of the prepared fluorescent materials into films, fibers, paper strips, carbon dots, hydrogels and solutions which are applied for the sensing of toxic metals and anions, pH, bioimaging, common organic solvents, aliphatic and aromatic amines, nitroaromatics, fluorescent printing, coating, and anti-counterfeiting applications. Finally, the discussion about the upcoming investigations, challenges, and options open for the cellulose-based luminescence sensors are communicated. We believe that this review will appeal more and more attention and curiosity for the chemists, biochemists, and chemical engineers working with the synthesis of cellulose-based fluorescent materials for widespread applications.

Smart Adsorbents for Aquatic Environmental Remediation

A noticeable interest and steady rise in research studies reporting the design and assessment of smart adsorbents for sequestering aqueous metal ions and xenobiotics has occurred in the last decade. This motivates compiling and reviewing the characteristics, potentials, and performances of this new adsorbent generation's metal ion and xenobiotics sequestration. Herein, stimuli-responsive adsorbents that respond to its media (as internal triggers; e.g., pH and temperature) or external triggers (e.g., magnetic field and light) are highlighted. Readers are then introduced to selective adsorbents that selectively capture materials of interest. This is followed by a discussion of self-healing and self-cleaning adsorbents. Finally, the review ends with research gaps in material designs.

Fabrication of a novel core-shell-shell temperature-sensitive magnetic composite with excellent performance for papain adsorption

Herein, a novel temperature-sensitive magnetic composite (Fe3O4@SiO2@P(NIPAM-co-VI)/Cu2+) with a uniform core-shell-shell structure was successfully prepared via a layer-by-layer method. The resulting magnetic composite revealed good magnetic properties and remarkable affinity to papain with a maximum adsorption capacity of 199.17 mg g-1. The adsorption equilibrium data fitted the pseudo-second-order kinetic and Freundlich models well, and the major thermodynamics parameters indicated that adsorption was an endothermic and spontaneous process. Fe3O4@SiO2@P(NIPAM-co-VI)/Cu2+ could thermally protect papain, which is attributed to the reversible hydrophilic-hydrophobic transition of the composite at temperatures below and above the lower critical solution temperature. More importantly, the magnetic composite could be recycled at least six times without a remarkable loss in its adsorption capacity, and the process of adsorption and elution had no significant effect on the activity and structure of papain. This work could provide a novel separation method for papain without loss of its activity.

Synthesis and characterization of poly(N-isopropylmethacrylamide-acrylic acid) smart polymer microgels for adsorptive extraction of copper(II) and cobalt(II) from aqueous medium: kinetic and thermodynamic aspects

Extraction of toxic heavy metal ions from aqueous medium using poly(N-isopropylmethacrylamide-acrylic acid) (P(NiPmA-Ac)) microgels as adsorbent has been investigated in present study. P(NiPmA-Ac) microgel particles were prepared by free radical precipitation polymerization in aqueous medium. Morphology and size of the prepared microgel particles was investigated by transmission electron microscopy (TEM). The Fourier transform infrared (FT-IR) analysis of pure and metal ion-loaded microgel particles was performed to confirm the presence of various functionalities of microgel particles and their interaction with metal ions extracted from aqueous medium. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to investigate the thermal stability and thermal behavior of pure and metal ion-loaded microgel particles. Contents of metal ions loaded into microgel particles were determined by TGA analysis. It was observed that P(NiPmA-Ac) particles have a potential to extract Cu²⁺ and Co²⁺ ions from aqueous medium. The Freundlich adsorption isotherm model best interprets the adsorption process as compared with the Langmuir model. Value of R² according to the Freundlich adsorption isotherm was found to be 0.994 and 0.993 for Cu²⁺ and Co²⁺ ions, respectively. Adsorption process was followed by pseudo second order kinetics for Cu²⁺ and Co²⁺ ions with R² values of 0.999 for both metal ions. Thermodynamic study showed that adsorption process was spontaneous, feasible, and endothermic in nature. Entropy was decreased at adsorbate-adsorbent interface during adsorption process. Adsorbent was recycled and reused for removal of Cu²⁺ ions, and adsorption efficiency was found to be maintained up to three cycles. Microgel particles also have ability to extract Cu²⁺ ions efficiently from electroplating wastewater. Graphical abstract.

Fabrication of Cellulose Nanocrystal-g-Poly(Acrylic Acid-Co-Acrylamide) Aerogels for Efficient Pb(II) Removal

In this work, cellulose nanocrystals (CNCs) obtained by the acid hydrolysis of waste bamboo powder were used to synthesize cellulose nanocrystal-g-poly(acrylic acid-co-acrylamide) (CNC-g-P(AA/AM)) aerogels via graft copolymerization followed by freeze-drying. The structure and morphology of the resulting aerogels were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and the CNC-g-P(AA/AM) aerogels exhibited excellent absorbent properties and adsorption capacities. Subsequent Pb(II) adsorption studies showed that the kinetic data followed the pseudo-second-order equation, while the adsorption isotherms were best described using the Langmuir model. The maximum Pb(II) adsorption capacity calculated by the Langmuir model reached up to 366.3 mg/g, which is a capacity that outperformed that of the pure CNC aerogel. The CNC-g-P (AA/AM) aerogels become structurally stable through chemical cross-linking, which enabled them to be easily regenerated in HCl solution and retain the adsorption capacity after repeated use. The aerogels were found to maintain 81.3% removal efficiency after five consecutive adsorption-desorption cycles. Therefore, this study demonstrated an effective method for the fabrication of an aerogel adsorbent with an excellent reusability in the effective removal of Pb(II) from aqueous solutions.

Fabrication and Optimization of the Thermo-Sensitive Hydrogel Carboxymethyl Cellulose/Poly(N-isopropylacrylamide-co-acrylic acid) for U(VI) Removal from Aqueous Solution

In this work, the thermo-sensitive materials N-isopropylacrylamide (NIPAM) and acrylic acid (AA) were crosslinked with carboxymethyl cellulose (CMC) (CMC/P (NIPAM-co-AA)) via a free radical polymerization method for the removal of U(VI) from aqueous solution. The L16 (45) orthogonal experiments were designed for the optimization of the synthesis condition. The chemical structures of the crosslinking hydrogel were confirmed by FTIR spectroscopy. The microstructural analyses were conducted though scanning electron microscopy (SEM) to show the pore structure of the hydrogel. The adsorption performance of the CMC/P (NIPAM-co-AA) hydrogel for the uptake of U(VI) from simulated wastewater was also investigated. The adsorption reached equilibrium within 1 h. Under the reaction of pH = 6 and a temperature of 298 K, an initial concentration of U(VI) of 5 mg·L-1, and 10 mg of the CMC/P(NIPAM-co-AA) hydrogel, the maximum adsorption capacity was 14.69 mg g-1. The kinetics fitted perfectly with the pseudo-second-order model, and the isotherms for the composite hydrogel adsorption of U(VI) was in accordance with the Langmuir model. The chemical modification confirmed that the acylamino group played an important role in uranium adsorption. The desorption and reusability study revealed that the resolution rate was still available at approximately 77.74% after five alternate heating cycles at 20 and 50 °C of adsorption-desorption.

Temperature and pH sensitive composite for rapid and effective removal of sulfonylurea herbicides in aqueous solution

Excessive pesticide residues in the environment have caused more and more serious social problems. In this article, the polymer materials and graphene oxide were smoothly grafted together through surface-initiated atom-transfer radical polymerization. A temperature and pH dual-sensitive adsorbent was successfully obtained, which was used for the removal of six sulfonylurea herbicides in the aquatic environment. Experiment results showed that the adsorbent could efficiently remove the tested pesticides in aqueous solution rapidly (only 1 min). The adsorption process was in consist with the pseudo-second-order kinetics equation and Freundlich model, and the thermodynamic parameters were also calculated. Furthermore, the mechanism for removal performance was judged as n-π, π-π, hydrogen bonding, hydrophobic and electrostatic interaction verdict. Exhilaratingly, the material showed no significant toxicity to Daphnia magna on risk assessment.

A biocomputing platform with electrochemical and fluorescent signal outputs based on multi-sensitive copolymer film electrodes with entrapped Au nanoclusters and tetraphenylethene and electrocatalysis of NADH

In this work, poly(N,N'-dimethylaminoethylmethacrylate-co-N-isopropylacrylamide) copolymer films were polymerized on the surface of Au electrodes with a facile one-step method, and Au nanoclusters (AuNCs) and tetraphenylethene (TPE) were synchronously embedded in the films, designated as P(DMA-co-NIPA)/AuNCs/TPE. Ferrocene dicarboxylic acid (FDA), an electroactive probe in solution displayed inverse pH- and SO42--sensitive on-off cyclic voltammetric (CV) behaviors at the film electrodes. The electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) mediated by FDA in solution could substantially amplify the CV response difference between the on and off states. Moreover, the two fluorescence emission (FL) signals from the TPE constituent at 450 nm and AuNCs component at 660 nm in the films also demonstrated SO42-- and pH-sensitive behaviors. Based on the aforementioned results, a 4-input/9-output biomolecular logic circuit was constructed with pH, Na2SO4, FDA and NADH as the inputs, and the CV signals and the FL responses at 450 and 660 nm at different levels as the outputs. Additionally, some functional non-Boolean devices were elaborately designed on an identical platform, including a 1-to-2 decoder, a 2-to-1 encoder, a 1-to-2 demultiplexer and different types of keypad locks. This work combines copolymer films, bioelectrocatalysis, and fluorescence together so that more complicated biocomputing systems could be established. This work may pave a new way to develop advanced and sophisticated biocomputing logic circuits and functional devices in the future.

Adsorption of Pb2+ from Aqueous Solutions Using Novel Functionalized Corncobs via Atom Transfer Radical Polymerization

The present study developed novel functionalized corncobs introducing brushes with dense and active carboxyl groups (-COOH), named MC-g-PAA, for the highly efficient adsorption of Pb2+ from aqueous solutions. MC-g-PAA were synthesized via atom transfer radical polymerization (ATRP) and characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The amount of Pb2+ adsorbed on MC-g-PAA by hydrolysis with t-BuOK was 2.28 times greater than that with NaOH, attributed to the larger steric effect of t-BuOK, which reduced the hydrolysis of the bromo-ester groups. The influence of different parameters including the solid/liquid ratio, working solution pH, sorption temperature, and initial concentration and sorption time on the adsorption of Pb2+ were investigated in detail in batch experiments. Thermodynamic studies have shown that the adsorption process was spontaneous, endothermic, and accompanied by an increase in randomness. A better fit for the isotherm data was obtained using the Langmuir model than for the other four models and the maximum amount ( q max ) of Pb2+ adsorbed on MC-g-PAA was 342.47 mg/g, which is 21.11 times greater when compared with that of pristine corncobs (16.22 mg/g). The adsorption of Pb2+ on MC-g-PAA was very fast and followed the pseudo-second-order kinetic equation with a correlation coefficient of 0.99999. This monolayer adsorption process was dominated by chemical adsorption, and may proceed according to complexation and electrostatic interactions between Pb2+ and the carboxylate groups. This study indicated that MC-g-PAA could be successfully used as an adsorbent for the removal of Pb2+ from aqueous solutions due to its excellent efficiency.

Thermoresponsive Bentonite for Water-Based Drilling Fluids

As an important industrial material, bentonite has been widely applied in water-based drilling fluids to create mud cakes to protect boreholes. However, the common mud cake is porous, and it is difficult to reduce the filtration of a drilling fluid at high temperature. Therefore, this paper endowed bentonite with a thermo response via the insertion of N-isopropylacrylamide (NIPAM) monomers. The interaction between NIPAM monomers and bentonite was investigated via Fourier infrared spectroscopy (FTIR), isothermal adsorption, and X-ray diffraction (XRD) at various temperatures. The results demonstrate that chemical adsorption is involved in the adsorption process of NIPAM monomers on bentonite, and the adsorption of NIPAM monomers accords with the D-R model. With increasing temperature, more adsorption water was squeezed out of the composite when the temperature of the composite exceeded 70 °C. Based on the composite of NIPAM and bentonite, a mud cake was prepared using low-viscosity polyanionic cellulose (Lv-PAC) and initiator potassium peroxydisulfate (KPS). The change in the plugging of the mud cake was investigated via environmental scanning electron microscopy (ESEM), contact angle testing, filtration experiments, and linear expansion of the shale at various temperatures. In the plugging of the mud cake, a self-recovery behavior was observed with increasing temperature, and resistance was observed at 110 °C. The rheology of the drilling fluid was stable in the alterative temperature zone (70-110 °C). Based on the high resistance of the basic drilling fluid, a high-density drilling fluid (ρ = 2.0 g/cm3) was prepared with weighting materials with the objective of drilling high-temperature formations. By using a high-density drilling fluid, the hydration expansion of shale was reduced by half at 110 °C in comparison with common bentonite drilling fluid. In addition, the rheology of the high-density drilling fluid tended to be stable, and a self-recovery behavior was observed.

Novel combined method of biosorption and chemical precipitation for recovery of Pb2+ from wastewater

A novel combined biosorption-precipitation process has been designed and applied to recycle Pb²⁺ from low concentration lead containing wastewater. Pb²⁺ was firstly removed selectively from wastewater by pyromellitic dianhydride (PMDA) modified sugarcane bagasse (SB) fixed-bed column, and then, it was desorbed into the concentrated eluate and recycled by adding chemical precipitant. Adsorption performance of the column and optimum desorption and precipitation condition for Pb²⁺ were investigated in detail. Results showed that the as-prepared column could efficiently remove Pb²⁺ from aqueous solution and optimum condition for Pb²⁺ precipitation in eluate was at pH 3.0 and molar ratio of precipitant to Pb²⁺ of 5:1 by using Na₃PO₄ as precipitant. Recovery experiment illustrated that Pb²⁺ was selectively removed from wastewater containing ions of Pb²⁺, Zn²⁺, Cd²⁺, Ca²⁺, K⁺, and Na⁺ through competitive substitution adsorption on the modified SB, and mass ratio of the five metal ions in eluate was 96.8:0.7:0.7:0.7:0.5:0.5. Pb²⁺ in this concentrated and purified eluate solution was recycled efficiently by adding Na₃PO₄. The combined method had great potential in application of heavy metal recovery from wastewater.