Genetic Engineering-Facilitated Coassembly of Synthetic Bacterial Cells and Magnetic Nanoparticles for Efficient Heavy Metal Removal

Heavy-metal pollution is becoming a worldwide problem severely threatening our health and ecosystem. In this study, we constructed a genetic-engineering-driven coassembly of synthetic bacterial cells and magnetic nanoparticles (MNPs) for capturing heavy metals. The Escherichia coli cells were genetically engineered by introducing a de novo synthetic heavy-metal-capturing gene (encoding a protein SynHMB containing a six-histidine tag, two cystine-rich peptides, and a metallothionein sequence) and a synthetic type VI secretory system (T6SS) cluster of Pseudomonas putida, endowing the synthetic cells (SynEc2) with high ability of displaying the heavy-metal-capturing SynHMB on cell surface. MNPs were synthesized by a coprecipitation method and further modified by polyethylenimine (PEI) and diethylenetriaminepentaacetic acid (DTPA). Owing to the surface exposure of six-histidine tag on the synthetic bacteria and carboxyl groups on the modified MNPs (MNP@SiO₂-PEI-DTPA), the synthetic bacterial cells and MNPs coassembled to form biotic/abiotic complex exhibiting a self-developing characteristic. In the culture medium containing both Cd²⁺ and Pb²⁺, the coassemblies captured these heavy metals with high removal efficiency (>90% even at 50 mg/L of Cd²⁺ and 50 mg/L of Pb²⁺) and were conveniently recycled by artificial magnetic fields. Moreover, the coassemblies realized coremoval of organic carbon pollutants with the removal efficiency of >80%. This study builds a novel biotic/abiotic coassembling platform facilitated by genetic engineering and sheds light on development of artificial magnetic biological systems for efficient treatment of environmental pollution.

Magnetically separable and recyclable bamboo-like carbon nanotube-based FRET assay for sensitive and selective detection of Hg2

The global occurrence of toxic hazards in aquatic ecosystems has aroused concern about the potential impacts on the ecological environment and human health in recent decades. Mercury(II) ions that originate from widespread sources including the mining industry, fossil fuel consumption, and industrial wastes are now well known as a highly toxic pollutant. Despite various detection methods which have been reported to sense Hg²⁺, it still poses a great challenge for us to develop a new effective sensing platform to replenish current fluorescent detection techniques. Here, we report a novel fluorescent biosensor using bamboo-like magnetic carbon nanotubes (BMCNTs) and FAM-labeled T-rich ssDNA for efficient detection of Hg²⁺ in aqueous solution. The proposed biosensor shows a good response toward Hg²⁺ detection over a linear response range of 0.05~1 μM (R² = 0.98) with a detection limit of 20 nM. It also exhibits the capability to discriminate Hg²⁺ ions with negligible response to other metal ions, such as Ca²⁺, Cd²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺. Interestingly, the BMCNTs could be separated and recycled easily by using an external magnet, which means a much more cost-effective, easy-to-operate, and eco-friendly method for Hg²⁺ ion detection.

Hydrogel-Based Gas Sensors for NO2 and NH3

In this study, an innovative gas sensing mechanism, self-responsive sensing mechanism, has been detected in the supramolecular hydrogel-based sensors. The self-responsive ability of as-fabricated hydrogel-based sensors to the target gas (e.g., NO₂, NH₃, etc.) is determined by three synergetic supramolecular interactions, namely, hydrogen bonding, molecule crystallization, and electrostatic interactions existing in hydroxyls, poly(vinyl alcohol) (PVA) crystallization, and poly(ionic liquids) of the intrinsic hydrogel networks, respectively. On account of unique synergetic supramolecular interactions, the sensors not only exhibit a rapid, reversible, and reproducible response but also show good tensile and compressive properties and excellent recovery property. The results demonstrate the potential of the self-responsive sensing mechanism as a pathway to realize a new generation of highly responsive hydrogel-based gas sensors.

Selective adsorption of Ag (Ⅰ) from aqueous solutions using Chitosan/polydopamine@C@magnetic fly ash adsorbent beads

A Chitosan/polydopamine@C@magnetic fly ash (CPCMFA) adsorbent bead was prepared for adsorption of Ag (Ⅰ) in aqueous solutions and exhibited good selectivity for Ag (Ⅰ) ion. To investigate its adsorption behaviors, equilibrium, kinetic and selective studies were conducted through batch experiments. Additionally, the influence of the pH value was also evaluated. In addition, the nature, composition, morphology, and magnetic property of the prepared adsorbent beads were characterized by Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating-sample magnetometry (VSM). The freeze-dry form of CPCMFA also exhibited high adsorption capacity and selectivity for Ag (Ⅰ), with a maximum adsorption capacity of 57.02 mg/g at pH 4 and 30 °C. The experimental data were well described by the Langmuir isotherm and elovich kinetic models. The thermodynamics parameters, ΔH = 10.653 kJ/mol, ΔS = 96.63 J/mol K and ΔG < 0, demonstrate that the adsorption of Ag (Ⅰ) on the freeze-dry form adsorbent is spontaneous and endothermic. Moreover, regeneration studies showed the high recyclability of the adsorbent, which after five cycles of use it was still able to adsorb 95.7% of the amount adsorbed by the fresh adsorbent.

Magnetic chitosan-copper nanocomposite: A plant assembled catalyst for the synthesis of amino- and N-sulfonyl tetrazoles in eco-friendly media

A greener, cost efficient and simple method is described to prepare copper nanoparticles (NPs) immobilized on the magnetic chitosan (one of the more versatile polysaccharides) using Euphorbia falcata leaf extract as reducing/stabilizing agent. The prepared catalyst (Cu NPs@Fe₃O₄-chitosan) was authenticated by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry/derivative thermogravimetry (TG/DTG), Vibrating sample magnetometer (VSM), and elemental mapping. TEM analysis indicates that Cu NPs with average sizes in 5-10 nm range is formed on magnetic chitosan with the spherical morphology. The Cu NPs@Fe₃O₄-chitosan was employed as a new catalyst for the synthesis of different tetrazoles by the reaction of various secondary or tertiary cyanamides with sodium azide in water under reflux conditions. Easy separation by external magnetic field, mild reaction conditions, low cost and the reusability are some of the beneficial features of this catalyst.

Preparation of magnetic hydrogel microspheres of lignin derivate for application in water

A low-cost and well-separated approach is introduced for adsorption pollutants in water. Chemical modified lignin is prepared with diethylenetriamine to enhance the reaction activities, then used to prepare lignin derivate magnetic hydrogel microspheres (LDMHMs) via blending with Fe₃O₄. The LDMHMs are successful prepared by the determination of FT-IR data, and the morphology shown from SEM imagine indicates the LDMHMs are in nanosized. The prepared LDMHMs are used as adsorbents for organic dyes, such as methylene blue (MB), methyl orange (MO) and malachite green (MG), the plateaus data are 43 mg/g, 39 mg/g and 155 mg/g, respectively. For inorganic pollutions, such as Pb²⁺, Hg²⁺ and Ni²⁺, the plateaus data are 33 mg/g, 55 mg/g and 23 mg/g, respectively. The adsorption data of unmodified lignin are 2.6 mg/g (Pb²⁺), 3.3 mg/g (Hg²⁺), 2.1 mg/g (Ni²⁺), 8 mg/g (MB), 10 mg/g (MG) and 2 mg/g (MO) in the same condition. The adsorbents are recycled by magnetic separation, regenerating from acid condition and reused for multiple cycles. The regeneration ratios are all above 90%, indicating a highly reusability and further reducing the cost of the treatment.

Fluorescent chitosan hydrogel for highly and selectively sensing of p-nitrophenol and 2, 4, 6-trinitrophenol

Nitroaromatic compounds, especially 2, 4, 6-trinitrophenol, have strong biological toxicity and explosive risks, so the detection of 2, 4, 6-trinitrophenol exhibit importantly practical and scientific significance. In this work, three fluorescence functionalized chitosan CNS 3, CNS 4 and CNS 5 were prepared using chitosan as matrix. When 2, 4, 6-trinitrophenol (TNP) and/or p-nitrophenol (4-NP) was present in spot, these fluorescent chitosan sensors produced notable fluorescence quenching. It renders the chitosan sensing ability to detect TNP and 4-NP selectively and sensitively. The sensing mechanism is investigated as well. When introduced electron-rich moieties to the fluorescent chitosan, the sensitive detecting ability could be obtained. Excellent recognition ability could reach as low as 0.28 μM. The fluorescence fictionalization cause slight influence to the gel performance of chitosan.

Lignin-based hydrogels: A review of preparation, properties, and application

Lignin as the second most abundant and the only polyaromatics-contained bio-polymer in plant has been most studied for various applications. In the past decade, the utilization of lignin for value-added materials has been extensively sought after since lignin valorization represents one of the main challenging issues of the paper industry and lignocellulosic biorefinery. Among these researches, making lignin into hydrogels has great potential for upgrading lignin into functional materials. In this review, lignin hydrogel is wrapped up with preparation strategies, properties and applications. The major cross-linking strategies to synthesize lignin-based hydrogels were reviewed first, including monomers copolymerization, crosslinking of monomers with reactive polymer precursors and polymer-polymer crosslinking. Two most important properties of mechanical and porous structures of lignin hydrogel were then discussed. More importantly, we extensively reviewed current applications of lignin hydrogel, including absorption, controlled release, smart materials for stimuli sensitive, biosensors and electrodes. These applications have paved avenues for lignin valorization. Overall, this paper covers recent advancements regarding lignin-based hydrogel and represents a timely review of this promising material.

Multifunctional nanocellulose/metal and metal oxide nanoparticle hybrid nanomaterials

Nanocellulose materials are derived from cellulose, the most abundant biopolymer on the earth. Nanocellulose have been extensively used in the field of food packaging materials, wastewater treatment, drug delivery, tissue engineering, hydrogels, aerogels, sensors, pharmaceuticals, and electronic sectors due to their unique chemical structure and excellent mechanical properties. On the other hand, metal and metal oxide nanoparticles (NP) such as Ag NP, ZnO NP, CuO NP, and Fe₃O₄ NP have a variety of functional properties such as UV-barrier, antimicrobial, and magnetic properties. Recently, nanocelluloses materials have been used as a green template for producing metal or metal oxide nanoparticles. As a result, multifunctional nanocellulose/metal or metal oxide hybrid nanomaterials with high antibacterial properties, ultraviolet barrier properties, and mechanical properties were prepared. This review emphasized recent information on the synthesis, properties, and potential applications of multifunctional nanocellulose-based hybrid nanomaterials with metal or metal oxides such as Ag NP, ZnO NP, CuO NP, and Fe₃O₄ NP. The nanocellulose-based hybrid nanomaterials have huge potential applications in the area of food packaging, biopharmaceuticals, biomedical, and cosmetics.

β-Cyclodextrin Polymers on Microcrystalline Cellulose as a Granular Media for Organic Micropollutant Removal from Water

Organic contaminants at low concentrations, known as micropollutants, are a growing threat to water resources. Implementing novel adsorbents capable of removing micropollutants during packed-bed adsorption is desirable for rapid water purification and other efficient separations. We previously developed porous polymers based on cyclodextrins that demonstrated rapid uptake and high affinity for dozens of micropollutants (MPs) in batch experiments. However, these polymers are typically produced as powders with irregular particle size distributions in the range of tens of micrometers. In this powdered form, cyclodextrin polymers cannot be implemented in packed-bed adsorption processes because the variable particle sizes yield insufficient porosity packing and consequently generate high back-pressure. Here we demonstrate a facile approach to remove micropollutants from water in a continuous manner by polymerizing cyclodextrin polymer networks onto cellulose microcrystals to provide a core/shell structure. Batch adsorption experiments demonstrate rapid pollutant uptake and high accessibility of the cyclodextrins on the adsorbent. Similarly, column experiments demonstrate rapid uptake of a model pollutant with minimal back-pressure, demonstrating potential for use in packed-bed adsorption processes. Furthermore, the pollutant-saturated columns were regenerated using methanol and reused three times with almost no change in performance. Column experiments conducted with a mixture of 15 micropollutants at environmentally relevant concentrations demonstrated that removal was determined by the affinity of each micropollutant for cyclodextrin polymers. The cyclodextrin polymer grafted onto cellulose microcrystals is more resistant to both anaerobic and aerobic biodegradation as compared to cyclodextrins and unmodified cellulose crystals, presumably due to the aromatic cross-linkers, demonstrating persistence. Collectively, the findings from this study demonstrate a general strategy to incorporate novel cyclodextrin adsorbents onto cellulose substrates to enable rapid and efficient removal of micropollutants during packed-bed adsorption as well as their promising long-term stability and regeneration capabilities.

Multifunctional cellulose-based hydrogels for biomedical applications

In recent decades, cellulose has been extensively investigated due to its favourable properties, such as hydrophilicity, low-cost, biodegradability, biocompatibility, and non-toxicity, which makes it a good feedstock for the synthesis of biocompatible hydrogels. The plentiful hydrophilic functional groups (such as hydroxyl, carboxyl, and aldehyde groups) in the backbone of cellulose and its derivatives can be used to prepare hydrogels easily with fascinating structures and properties, leading to burgeoning research interest in biomedical applications. This review focuses on state-of-the-art progress in cellulose-based hydrogels, which covers from their preparation methods (including chemical methods and physical methods) and physicochemical properties (such as stimuli-responsive properties, mechanical properties, and self-healing properties) to their biomedical applications, including drug delivery, tissue engineering, wound dressing, bioimaging, wearable sensors and so on. Moreover, the current challenges and future prospects for cellulose-based hydrogels in regard to their biomedical applications are also discussed at the end.

Two combined mechanisms responsible to hexavalent chromium removal on active anaerobic granular consortium

Hexavalent chromium (Cr VI) from industrial wastewaters represents a highly toxic source at low concentrations. Biological treatments with anaerobic granular biomass are a promising alternative for the Cr VI bioremediation. This study evaluated the Cr VI removal in a range of 5-500 mg/L, using an active anaerobic granular consortium. Two removal mechanisms were differentiated from the assays: 1) biological reduction of 70 mg/L to Cr III at a concentration of 250 mg Cr VI/L and 2) physical bioadsorption of 297 mg of Cr VI/L or 31.39 mg of Cr VI/g_biomass at concentration of 500 mg Cr VI /L. The half-maximal inhibitory concentration (IC₅₀) values for the rate and production of methane were 1.4 and 253 mg/L, respectively. In addition, Cr VI is a biostimulant that increase the methane production, in a range from 5 to 100 mg/L, of the anaerobic consortium. This work demonstrates the potential application of the anaerobic granular consortium in metal bioremediation.

Magnetic Mesoporous Carbons Derived from in Situ MgO Template Formation for Fast Removal of Heavy Metal Ions

In this paper, magnetic mesoporous carbon composites were prepared by calcination of the mixture of magnesium citrate and Fe₃O₄@SiO₂ in an inert atmosphere. A high content of Fe₃O₄@SiO₂ and MgO was in situ embedded in a carbon matrix. After removing the MgO template by diluted acid, the resulting material (Fe₃O₄@SiO₂@mC) was subjected to further H₂O₂ oxidation treatment. The formed oxygen-containing functional groups on the products provided plenty of active sites for the adsorption of analytes of interest. The obtained composites (Fe₃O₄@SiO₂@mC-H₂O₂) exhibited a mesoporous structure with a high specific surface area of 731 m² g^-1. The adsorption capacities of Fe₃O₄@SiO₂@mC-H₂O₂ for Cu(II) and Pb(II) were calculated to be 86.5 and 156 mg g^-1, respectively. Under optimal conditions, the adsorption isotherm of Cu(II) and Pb(II) onto Fe₃O₄@SiO₂@mC-H₂O₂ fitted the Langmuir model and the adsorption kinetic was well-correlated with the pseudo-second-order model. Besides, Fe₃O₄@SiO₂@mC-H₂O₂ exhibited fast removal dynamics (within less than 1 min) for Cu(II) and Pb(II), demonstrating great application potential in wastewater treatment.

CQDs-Doped Magnetic Electrospun Nanofibers: Fluorescence Self-Display and Adsorption Removal of Mercury(II)

This paper reports the carbon quantum dots-doped magnetic electrospinning nanofibers for the self-display and removal of Hg(II) ions from water. The fluorescent carbon quantum dots and magnetic Fe₃O₄ nanoparticles were pre-prepared successfully, and they appeared to be homogeneously dispersed in nanofibers via electrospinning. During the sorption of Hg(II) ions, the significant fluorescence signals of nanofibers gradually declined and exhibited a good linear relationship with cumulative adsorption capacity, which could be easily recorded by the photoluminescence spectra. The sorption performance of mercury ions onto the nanofibers was investigated in terms of different experimental factors including contact time, solution pH value, and initial ion concentration. Considering the actual parameters, the nanofibers were sensitive self-display adsorption system for Hg(II) ions in the existence of other cation. The sorption data were described by different kinetic models, which indicate that the whole sorption was controlled by chemical adsorption. The intraparticle diffusion mass transfer was not obvious in this system, which further proved the uniform adsorption and even fluorescence quenching in nanofibers. Additionally, the nanocomposite fiber could regenerate in several cycles with no significant loss of adsorption capacity and fluorescence intensity. Thus, the nanofibers are promising alternatives for environmental pollution incidents. It is especially competent due to its high efficiency for self-display and removal of high concentration of mercury ions.

Chitosan-Cellulose Multifunctional Hydrogel Beads: Design, Characterization and Evaluation of Cytocompatibility with Breast Adenocarcinoma and Osteoblast Cells

Cytocompatible polysaccharide-based functional scaffolds are potential extracellular matrix candidates for soft and hard tissue engineering. This paper describes a facile approach to design cytocompatible, non-toxic, and multifunctional chitosan-cellulose based hydrogel beads utilising polysaccharide dissolution in sodium hydroxide-urea-water solvent system and coagulation under three different acidic conditions, namely 2 M acetic acid, 2 M hydrochloric acid, and 2 M sulfuric acid. The effect of coagulating medium on the final chemical composition of the hydrogel beads is investigated by spectroscopic techniques (ATR–FTIR, Raman, NMR), and elemental analysis. The beads coagulated in 2 M acetic acid displayed an unchanged chitosan composition with free amino groups, while the beads coagulated in 2 M hydrochloric and sulfuric acid showed protonation of amino groups and ionic interaction with the counterions. The ultrastructural morphological study of lyophilized beads showed that increased chitosan content enhanced the porosity of the hydrogel beads. Furthermore, cytocompatibility evaluation of the hydrogel beads with human breast adenocarcinoma cells (soft tissue) showed that the beads coagulated in 2 M acetic acid are the most suitable for this type of cells in comparison to other coagulating systems. The acetic acid fabricated hydrogel beads also support osteoblast growth and adhesion over 192 h. Thus, in future, these hydrogel beads can be tested in the in vitro studies related to breast cancer and for bone regeneration.

Aerogels from Chitosan Solutions in Ionic Liquids

Chitosan aerogels conjugates the characteristics of nanostructured porous materials, i.e., extended specific surface area and nano scale porosity, with the remarkable functional properties of chitosan. Aerogels were obtained from solutions of chitosan in ionic liquids (ILs), 1-butyl-3-methylimidazolium acetate (BMIMAc), and 1-ethyl-3-methyl-imidazolium acetate (EMIMAc), in order to observe the effect of the solvent in the structural characteristics of this type of materials. The process of elaboration of aerogels comprised the formation of physical gels through anti-solvent vapor diffusion, liquid phase exchange, and supercritical CO₂ drying. The aerogels maintained the chemical identity of chitosan according to Fourier transform infrared spectrophotometer (FT-IR) spectroscopy, indicating the presence of their characteristic functional groups. The internal structure of the obtained aerogels appears as porous aggregated networks in microscopy images. The obtained materials have specific surface areas over 350 m²/g and can be considered mesoporous. According to swelling experiments, the chitosan aerogels could absorb between three and six times their weight of water. However, the swelling and diffusion coefficient decreased at higher temperatures. The structural characteristics of chitosan aerogels that are obtained from ionic liquids are distinctive and could be related to solvation dynamic at the initial state.

Hematite nanoparticle clusters with remarkably high magnetization synthesized from water-treatment waste by one-step “sharp high-temperature dehydration”

Hematite (α-Fe₂O₃) nanoparticle clusters with an exceptionally high magnetization of 51 emu g⁻¹ were synthesized for the first time. This material was prepared from water-treatment waste by a new “sharp high-temperature dehydration” process.

Potassium fulvate-functionalized graft copolymer of polyacrylic acid from cellulose as a promising selective chelating sorbent

(Cell-g-PAA)/KF is a promising selective chelating graft copolymer for heavy metal ions from aqueous solutions.

Cube sugar-like sponge/polymer brush composites for portable and user-friendly heavy metal ion adsorbents

Portable, non-toxic, and user-friendly sponge composites decorated with polyelectrolyte (PE) brushes were developed for the fast and efficient removal of heavy metal ions from waste water or drinking water. The polyacrylamide (PAM) and polyacrylic acid (PAA) brushes were grafted onto the sponge via "grafting-from" polymerization. For the polyethyleneimine (PEI) brush, "grafting-to" polymerization was used. A polydopamine (Pdop) layer was first coated on the sponge. Then, PEI was grafted onto the Pdop-coated sponge via a Michael addition reaction. The PEI-grafted sponge exhibited the best adsorption capacity and the fastest reaction rate of all the brushes due to the numerous adsorption sites of the PEI. The adsorption performance of two different PEI-grafted sponges depended on the molecular weight (MW) of the PEI. Simply by being dipped into a glass of water, non-toxic PEI-grafted sponge instantly removed the low concentration heavy metal ions, demonstrating a practical application for individual users.

Shell Biorefinery: Dream or Reality?

Shell biorefinery, referring to the fractionation of crustacean shells into their major components and the transformation of each component into value-added chemicals and materials, has attracted growing attention in recent years. Since the large quantities of waste shells remain underexploited, their valorization can potentially bring both ecological and economic benefits. This Review provides an overview of the current status of shell biorefinery. It first describes the structural features of crustacean shells, including their composition and their interactions. Then, various fractionation methods for the shells are introduced. The last section is dedicated to the valorization of chitin and its derivatives for chemicals, porous carbon materials and functional polymers.

Carboxyl-Functionalized Ionic Liquid Assisted Preparation of Flexible, Transparent, and Luminescent Chitosan Films as Vapor Luminescent Sensor

Herein we present a novel method to synthesize flexible self-standing films consisting of europium(III) complexes in nanoclay and chitosan, which are transparent and luminescent. Preparation takes place under aqueous conditions assisted by a carboxyl-functionalized ionic liquid (IL). The latter is used not only as a replacement for acetic acid to dissolve chitosan but, surprisingly, also to enhance the luminescence efficiency of the final films. A brighter luminescence is observed for the films prepared assisted with the ionic liquids compared to those by using acetic acid. The reason is that the ionic liquid used to dissolve chitosan can decrease proton strength on embedded platelets primarily through ion-exchange process and thus can increase the coordination number of europium(III) complexes. Exposure of the films to Et3N vapors can cause a further remarkable luminescence enhancement, while significant luminescence quenching occurred upon exposure to HCl vapors. The films are promising for applications in areas such as optoelectronics and vapor-sensitive luminescent sensors.

A review on chitosan-cellulose blends and nanocellulose reinforced chitosan biocomposites: Properties and their applications

Chitin is one of the most abundant natural polymers in world and it is used for the production of chitosan by deacetylation. Chitosan is antibacterial in nature, non-toxic, and biodegradable thus it can be used for the production of biodegradable film which is a green alternative to commercially available synthetic counterparts. However, their poor mechanical and thermal properties restricted its wide spread applications. Chitosan is highly compatible with other biopolymers thus its blending with cellulose and/or incorporation of nanofiber isolated from cellulose namely cellulose nanofiber and cellulose nanowhiskers are generally useful. Cellulosic fibers in nano scale are attractive reinforcement in chitosan to produce environmental friendly composite films with improved physical properties. Thus chitosan based composites have wide applicability and potential in the field of biomedical, packaging and water treatment. This review summarises properties and preparation procedure of chitosan-cellulose blends and nano size cellulose reinforcement in chitosan bionanocomposites for different applications.