Synthesis of organic-solvent-soluble cellulose and preparation of fluorescent polyurethanes for the detection and removal of Hg+ ions.

Modifying cellulose to obtain materials with favorable processing properties and functions is highly significant, especially, for the detection and removal of heavy metal ions. In this study, fluorescent cellulose-based polyurethane (PU) films containing naphthalimide fluorophore were synthesized and could use for the convenient detection and removal of Hg+ ions. Firstly, the microcrystalline cellulose was treated with SOCl2 to convert some -OH groups into -Cl. Simultaneously, a naphthalimide derivative (NAN) with -NH- groups was synthesized. Subsequently, a fluorescent cellulose-based probe (Cel-NAN) was prepared by utilizing the substitution reaction between -Cl on cellulose and -NH- on NAN. Finally, two cellulose-based fluorescent PU films (Cel-NAN-PU1 and Cel-NAN-PU2) were successfully synthesized by reacting the unreacted -OH groups on Cel-NAN with PEG-1000 and HDI/IPDI. These as-prepared PU films could serve as portable fluorescence test papers to Hg+ ions in aqueous solutions. Upon contact with Hg+ ions, the fluorescence was quenched, acting as a "turn-off" probe. Simultaneously, these films could serve as adsorbents for the removal of Hg+ ions from aqueous systems. Cel-NAN-PU1 film exhibited a removal efficiency over 80 % and an adsorption capacity of 8.4 mg·cm-2 for Hg+. These cellulose-based fluorescent PU films possess promising potential in the field of mercury pollution control.

Readily soluble cellulose-based fluorescent probes for the detection and removal of Fe3+ ion.

Cellulose is an economical, biodegradable, widely available, and eco-friendly natural macromolecule. But its utilization has been restricted due to its insolubility in water and common organic solvents. In this work, soluble fluorescent probes based on cellulose were synthesized. Firstly, the primary hydroxyl group in glucose units was reacted with SOCl2 to introduce Cl and obtain chloro-cellulose (Cell-Cl). This operation breaks down the regular structure and hydrogen bonding of the original cellulose, enabling it to dissolve in DMSO. Secondly, the Cell-Cl reacted with CS2 and 2-mercaptobenzothiazole to obtain a cellulose-based macromolecular RAFT reagent (Cell-CTA). Finally, the fluorescent monomers which bears -C=C- and naphthalimide, and methacrylic acid (MAA) were grafted onto the main chain of cellulose through RAFT polymerization. Thus, cellulose-based readily soluble macromolecular fluorescent probes were obtained. The cellulose-based probes can specifically recognize Fe3+ in pure water and can be recycled and regenerated. Additionally, the cellulose-based probes exhibit remarkable adsorption and separation properties for Fe3+ ions. The modification of cellulose decreases its crystallinity and introduces hydrophilic groups and fluorophores, which enables cellulose to be soluble in both pure water and the organic solvent DMSO. This work expands the application range of cellulose-based copolymers.

A novel method to prepare water-soluble cellulose-based fluorescent probes for highly sensitive and selective detection and removal of Hg2+/Hg22+ ions.

Improving the water solubility of natural product cellulose and using it to treat heavy metal ions is very important. In this work, cellulose-based fluorescent probes containing BODIPY fluorophore were synthesized by simple chemical method, which realized the selective recognition and removal of Hg2+/Hg22+ ions in an aqueous system. Firstly, fluorescent small molecule (BOK-NH2) bearing -NH2 group was synthesized through Knoevenagel condensation reaction between BO-NH2 and cinnamaldehyde. Secondly, via the etherification of -OH on the cellulose, substituents bearing -C ≡ CH groups with different lengths at the end are grafted on the cellulose. Finally, cellulose-based probes (P1, P2, and P3) were prepared by amino-yne click reaction. The solubility of cellulose is improved greatly, especially the cellulose derivative with branched long chains has excellent solubility in water (P3). Benefiting from the improved solubility, P3 could be processed into solutions, films, hydrogels, and powders. Upon the addition of Hg2+/Hg22+ ions, the fluorescence intensity enhanced, which are "turn-on" probes. At the same time, the probes could be utilized as efficient adsorbents for Hg2+/Hg22+ ions. The removal efficiency of P3 for Hg2+/Hg22+ is 79.7 %/82.1 %, and the adsorption capacity is 159.4 mg·g-1/164.2 mg·g-1. These cellulose-based probes are expected to be employed in the treatment of polluted environments.

Water-soluble chitosan-g-PMAm (PMAA)-Bodipy probes prepared by RAFT methods for the detection of Fe3+ ion.

It is a challenge to achieve the fully water-soluble chitosan. In this work, water-soluble chitosan-based probes were obtained by the following steps: boron-dipyrrolemethene (BODIPY)-OH was synthesized, and then BODIPY-OH was halogenated to BODIPY-Br. Afterwards, BODIPY-Br reacted with carbon disulfide and mercaptopropionic acid to obtain BODIPY-disulfide. BODIPY-disulfide was introduced to chitosan via amidation reaction to obtain fluorescent chitosan-thioester (CS-CTA); it is employed as the macro-initiator. Methacrylamide (MAm) was grafted onto chitosan fluorescent thioester through reversible addition-fragmentation chain transfer (RAFT) polymerization method. Thus, a water-soluble macromolecular probe (CS-g-PMAm) with chitosan as the main chain and PMAm as long-branched chains was obtained. It greatly improved the solubility in pure water. The thermal stability was reduced slightly, and the stickiness was greatly reduced and the samples displayed the characteristics of liquid. CS-g-PMAm could detect Fe3+ in pure water. By the same method, CS-g-PMAA (CS-g-Polymethylacrylic acid) was synthesized and investigated as well.

Organic-soluble chitosan-g-PHMA (PEMA/PBMA)-bodipy fluorescent probes and film by RAFT method for selective detection of Hg2+/Hg+ ions.

Chitosan as the plentiful and easily available natural polymer, its solubility in organic solvents is still a challenge. In this article, three different chitosan-based fluorescent co-polymers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. They could not only dissolve in several organic solvents, but also could selectively recognize Hg2+/Hg+ ions. Firstly, allyl boron-dipyrrolemethene (bodipy) was prepared, and used as one of the monomers in the subsequent RAFT polymerization. Secondly, chitosan-based chain transfer agent (CS-RAFT) was synthesized through classical reactions for dithioester preparation. Finally, three methacrylic ester monomers and bodipy bearing monomers were polymerized and grafted as branched-chains onto chitosan respectively. By RAFT polymerization, three chitosan-based macromolecular fluorescent probes were prepared. These probes could be readily dissolved in DMF, THF, DCM, and acetone. All of them exhibited the 'turn-on' fluorescence with selective and sensitive detection for Hg2+/Hg+. Among them, chitosan-g-polyhexyl methacrylate-bodipy (CS-g-PHMA-BDP) had the best performance, its fluorescence intensity could be increased to 2.7 folds. In addition, CS-g-PHMA-BDP could be processed into films and coatings. When loading on the filter paper, fluorescent test paper was prepared and it could realize the portable detection of Hg2+/Hg+ ions. These organic-soluble chitosan-based fluorescent probes could enlarge the applications of chitosan.

TEGylated Phenothiazine-Imine-Chitosan Materials as a Promising Framework for Mercury Recovery.

This paper reports new solid materials based on TEGylated phenothiazine and chitosan, with a high capacity to recover mercury ions from aqueous solutions. They were prepared by hydrogelation of chitosan with a formyl derivative of TEGylated phenothiazine, followed by lyophilization. Their structural and supramolecular characterization was carried out by 1H-NMR and FTIR spectroscopy, as well as X-ray diffraction and polarized light microscopy. Their morphology was investigated by scanning electron microscopy and their photophysical behaviour was examined by UV/Vis and emission spectroscopy. Swelling evaluation in different aqueous media indicated the key role played by the supramolecular organization for their hydrolytic stability. Mercury recovery experiments and the analysis of the resulting materials by X-ray diffraction and FTIR spectroscopy showed a high ability of the studied materials to bind mercury ions by coordination with the sulfur atom of phenothiazine, imine linkage, and amine units of chitosan.

Facile method to synthesize fluorescent chitosan hydrogels for selective detection and adsorption of Hg2+/Hg.

Fluorescent chitosan-based hydrogel for the selective detection and adsorption of Hg2+/Hg+ in aqueous environment was prepared through three-step synthesis strategy. NO2-Boron-dipyrrolemethene (BODIPY) was prepared firstly, and then the -NO2 group was reduced to -NH2 group. Finally, the NH2-BODIPY was introduced to chitosan by Schiff base formation reaction through bi-aldehyde. Eventually, fluorescent chitosan hydrogel was obtained. The as-prepared fluorescent hydrogel probe could detect Hg2+/Hg+ through PET mechanism with the detection limit of 0.3 µM. The recognition site which combines Hg2+/Hg+ is CN, it is just formed in the reaction with chitosan and the amino group on BODIPY. Adsorption capacity of the fluorescent hydrogel is 121 mg·g-1, which is almost seven times of the original chitosan. The isotherm and kinetics of Hg2+/Hg+ removal follows Langmuir isotherm and pseudo-second order kinetics, respectively. Besides, a series of fluorescent hydrogels were prepared to compare the elasticity, hydropHilicity, fluorescence intensity and adsorption capacity.

Imination of Microporous Chitosan Fibers-A Route to Biomaterials with "On Demand" Antimicrobial Activity and Biodegradation for Wound Dressings.

Microporous chitosan nanofibers functionalized with different amounts of an antimicrobial agent via imine linkage were prepared by a three-step procedure including the electrospinning of a chitosan/PEO blend, PEO removal and acid condensation reaction in a heterogeneous system with 2-formylphenylboronic acid. The fibers' characterization was undertaken keeping in mind their application to wound healing. Thus, by FTIR and 1H-NMR spectroscopy, it was confirmed the successful imination of the fibers and the conversion degree of the amine groups of chitosan into imine units. The fiber morphology in terms of fiber diameter, crystallinity, inter- and intra-fiber porosity and strength of intermolecular forces was investigated using scanning electron microscopy, polarized light microscopy, water vapor sorption and thermogravimetric analysis. The swelling ability was estimated in water and phosphate buffer by calculating the mass equilibrium swelling. The fiber biodegradation was explored in five media of different pH, corresponding to different stages of wound healing and the antimicrobial activity against the opportunistic pathogens inflicting wound infection was investigated according to standard tests. The biocompatibility and bioadhesivity were studied on normal human dermal fibroblast cells by direct contact procedure. The dynamic character of the imine linkage of the functionalized fibers was monitored by UV-vis spectroscopy. The results showed that the functionalization of the chitosan microporous nanofibers with antimicrobial agents via imine linkage is a great route towards bio-absorbable wound dressings with "on demand" antimicrobial properties and biodegradation rate matching the healing stages.

Fluorescent chitosan-BODIPY macromolecular chemosensors for detection and removal of Hg2+ and Fe3+ ions.

The detection of heavy metals, such as Hg2+ and Fe3+, is of great significance. In this work, fluorescent small-molecule BODIPY (BY-3) bearing CC group was synthesized firstly. And then, the chitosan-based polymer sensor CY-1 was synthesized through the spontaneous NH2/C≡C click reaction. The synthesized CY-1 can effectively bind and recognize Hg2+/Hg+ by the -C=N groups formed in the click reaction. Moreover, the macromolecular sensors CS-1 and CS-2 were synthesized by incorporating another recognition sites to CY-1. These synthesized macromolecular sensors can not only recognize Hg2+/Hg+, but also effectively recognize Fe3+/Fe2+. All of them exhibited significant quenching effect, visible to the naked eye under UV irradiation. The detection limit of CY-1 for Hg2+ was 1.51 × 10-6 mol/L, and the detection limit of CS-2 for Fe3+ was 2.30 × 10-6 mol/L. The BODIPY-chitosan sensors synthesized in this work have the functions of removing heavy metal ions besides the identifying ability. The maximum adsorption capacity of 1 g chitosan to Hg2+ was 108 mg as the best one. This article provides a new method to prepare macromolecular sensors for the detection and removal of heavy metal ions. As a useful natural polymer, chitosan's application scope was enlarged.

Fluorescent dialdehyde-BODIPY chitosan hydrogel and its highly sensing ability to Cu2+ ion.

Fluorescent hydrogel with proper hydrophilicity and thermal stability, excellent sensitivity and high selectivity has important practical and scientific significance, especially in heavy metal ion detection. In this work, by adjusting the content of [2, 6-Bis-[4-formylthiophene]]-1,3,5,7-tetramethyl-8-phenyl-4, 4-difluoroborazaindoloene (B3), as a cross-linking agent, a series of chitosan- fluoroboron dipyrrole-chitosan-based fluorescent hydrogels (CBC) with large stokes shift were designed and prepared. The hydrogels can be used as fluorescent probes for identifying Cu2+ in aqueous solution. The linear quenching range of Cu2+ is 0-50 µM, and the detection limit and quenching constant are 4.75 µM and 3.52 × 104 M-1, respectively. Under the interaction of Cu2+, the imine bond CN was converted to C- N bond, which causes the phenomenon of fluorescence quenching. In addition, relatively high crosslink density improves hydrophilicity and thermal stability of initial chitosan, and made the swelling ability better.

Chitosan based macromolecular probes for the selective detection and removal of Fe3+ ion.

Chitosan has been widely used due to its biodegradable, cost-effective and environmentally friendly properties. Modification of chitosan attracts much attention as promising methods to detect and remove organic and inorganic pollutants. In this work, chitosan-based macromolecular probes were designed and synthesized. The probes can detect Fe3+ in the presence of other metal ions. The detection mechanism is investigated as well. The probe's fluorescence quenching upon the addition of Fe3+ ion could be ascribed to the complexation between the electron-deficient ion Fe3+ and "C=N" (electron-rich group) of fluorescent chitosan probes. What's more, the obtained fluorescent macromolecular probes can be used for the removal of Fe3+ in solution. The probes could adsorb the Fe3+ in solution and the removal efficiency can reach as high as 62.0% while the removal efficiency of original chitosan is only 16.0%. The probes have good selective detection for Fe3+ and the detection limit reaches 1.2 µM.

Reaction-based highly selective and sensitive monomer/polymer probes with Schiff base groups for the detection of Hg2+ and Fe3+ ions.

It is urgent and important to detect heavy metals in environments. In this work, novel reaction-based fluorescent probes were obtained by Schiff base reaction. The probes with Schiff base moiety (-C=N-) undergo irreversible hydrolysis in the presence of Hg2+ and Fe3+. They exhibit perfect high selectivity and sensitivity to Hg2+and Fe3+ ions. Upon the addition of Hg2+and Fe3+, fluorescence intensity of the probes increased notably. And the color of the probe changes from brown to bright green under UV light, which can realize "naked eye" detection. In addition, Schiff base group was introduced into polyurethane chain through condensation polymerization reaction. As expected, the fluorescent polyurethane probe (P2) maintained the detection performance of its original small molecules (BSD). Even more P2 showed a more sensitive detection effect than BSD, and the detection limits of P2 for Hg2+ and Fe3+ reach 0.19 µM and 0.21 µM, respectively. It indicates that Reaction-based probes could be a useful tool for the detection of Hg2+ and Fe3+.

Phenothiazine-chitosan based eco-adsorbents: A special design for mercury removal and fast naked eye detection.

The aim of the paper was to investigate the ability of an eco-friendly luminescent xerogel prepared by chitosan crosslinking with a phenothiazine luminogen to detect and remove heavy metals. Its ability to give a divergent morphological and optical response towards fifteen environmental relevant metals was investigated by naked eye and UV lamp, fluorescence spectroscopy and scanning electron microscopy. A distinct response was noted for mercury, consisting in the transformation of the xerogel into a rubber-like material accompanied by the red shifting of the color of emitted light from yellow-green to greenish-yellow domain. The particularities of the metals anchoring into the xerogel were analyzed by FTIR spectroscopy and X-ray diffraction. The morphological changes and the metal uptake were analyzed by SEM-EDAX, swelling and gravimetric methods. It was concluded that mercury has a superior affinity towards this heteroatoms rich system, leading to a secondary crosslinking. This directed a great absorption capacity of 1673 mg/g and a specific morphological response for mercury ion concentrations up to 0.001 ppm.

Highly sensitive and selective fluorescent monomer/polymer probes for Hg2+ and Ag+ recognition and imaging of Hg2+ in living cells.

The detection of heavy metals such as Hg2+ and Ag+ is important and urgent. In this work, - NO2/- NH2/C=S boron dipyrromethene small molecular derivatives were synthesized at first. Then they were incorporated into polymer chains. The macromolecular fluorescent probes were obtained via Sonogashira reaction using the small molecular probes as building blocks. The as-prepared small-molecule fluorescent probe BO3 exhibits high sensing performance for Hg2+. By introducing it into macromolecules, the sensing ability still remains, and even more, the recognition performance is improved. The macromolecular fluorescent probes P1, P2, and P3 also have high recognition ability for Ag+ with a binding ratio of 2:1 (metal ion to probe ratio). Through the study of the sensing mechanism and the recycling experiments, it is found that the probes responded by the photo-induced electron transfer mechanism and can be recycled and reused. At the same time, BO3, P2, and P3 show excellent recognition performance for Hg2+ in living cells and zebrafish. Living cell imaging experiments indicated that these fluorescent probes had good cell membrane permeability and low cytotoxicity, and could realize bioimaging of Hg2+. Therefore, the application value of these fluorescent probes could be enlarged. Graphical abstract.

A polymer membrane tethered with a cycloruthenated complex for colorimetric detection of Hg2+ ions.

A new cyclometallated ruthenium complex (Ru1) involving a 2-(2-thienyl)pyridine and a benzo[e]indolium block connected with a hexanoic acid was successfully synthesized and characterized, which exhibited the high sensitivity and selectivity to Hg2+ over other common metal ions with the detection limit of as low as 0.053 µM in aqueous system. Then, it was grafted onto a polymer membrane to afford a Hg2+-sensitive membrane (sensor 1), which was characterized by FT-IR, SEM and XPS spectra, respectively. When sensor 1 was dipped into the aqueous solution of Hg2+ ions, the color of the membrane changed from dark-red to yellow, which could be observed by naked eyes easily. It should be noted that the membrane can absorb Hg2+ ions well in aqueous solution and the adsorption capacity of this polymer membrane for Hg2+ ions was determined by atomic absorption spectroscopy, indicating that it also could be used as a potential material for removal of Hg2+ ions.

Highly selective ratiometric fluorescent probes for the detection of Fe3+ and its application in living cells.

It's of vital importance to detect heavy metals in environment and living cells. In this work, four near-infrared regions boron dipyrromethene (BODIPY) probes (QBPH, PBPH, QBP and PBP) are constructed based on two BODIPY precursors (QB, PB) for sensing of Fe3+. As expected, these four probes exhibit obvious colorimetric and ratiometric response to Fe3+. In addition, QBP and PBP display highly sensitive and selective performance for detection of Fe3+. More importantly, QBP and PBP are successfully applied to near infrared imaging and detection of Fe3+ in living A549 cells; it indicates that these novel designed probes could be a useful tool for the studies of Fe3+ in living cells.

Fluorescent Porous Silica Microspheres for Highly and Selectively Detecting Hg2+ and Pb2+ Ions and Imaging in Living Cells.

In this work, SiO2 microspheres were first prepared by a conventional Stöber method and then etched by NaOH solution to obtain porous ones. By tuning the degree of etching, specific surface area of SiO2 microspheres could be controlled. Then, small fluorescent molecules are synthesized and incorporated onto the surface and/or pores of the SiO2 via layer-by-layer reaction to obtain fluorescent microspheres, namely, SiO2-NH2-BODIPY (SiNBB), SiO2-NH2-BODIPY-indole-benzothiazole (SiNBIT), and SiO2-NH2-BODIPY-indole-benzoxazole (SiNBIO). The as-prepared microspheres SiNBB exhibit highly sensitive and selective recognition ability for Hg2+ and Pb2+. When SiNBB encounters Hg2+ and Pb2+, the fluorescence intensity of SiNBB is increased up to fivefold. SiNBIT and SiNBIO are solely sensitive to Hg2+, and both have a single high sensitivity to recognize Hg2+. The adsorption efficiency of Hg2+ by the three fluorescent microspheres SiNBB, SiNBIT, and SiNBIO reached 2.91, 0.99, and 0.98 g/g of microspheres, respectively. Experimental results of A549 cells and zebrafish indicate that the fluorescent microspheres are permeable to cell membranes and organisms. The distribution of Hg2+ in the brain of zebrafish was obtained by the fluorescence confocal imaging technique, and Hg2+ was successfully detected in A549 cells and zebrafish.

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.

Facile Fabrication of Porous ZnS and ZnO Films by Coaxial Electrospinning for Highly Efficient Photodegradation of Organic Dyes.

Porous ZnS and ZnO nano-crystal films were fabricated via a three-step procedure. First, Zn(CH3 COO)2 /Silk Fibroin nanofiber mats were prepared by coaxial electrospinning. Second, Zn(CH3 COO)2 /Silk Fibroin mats were immersed in NaS solution to react with S2- to obtain ZnS/Silk Fibroin nanofiber mats. Finally, ZnO porous films were prepared by calcination of ZnS/Silk Fibroin composite mat at 600°C in air atmosphere. When ZnS/Silk Fibroin mats were calcinated in nitrogen, ZnS/Carbon composite mats were obtained accordingly. The resulting porous films were fully characterized. The ZnO porous films were the aggregation of ZnO nano-crystal with hexagonal wurtzite structure. The seize of ZnO was estimated in the range of 10-20 nm. Both of the ZnS and ZnO nano-crystal films exhibited high photocatalytic activities for the photodegradation of Methylene blue and Rhodamine B. It was also found that ZnO porous films are better than ZnS/Carbon nanofiber mats. In addition, photocatalysis of a real wastewater sample from a printing and dyeing company was conducted. The ZnO porous films exhibited excellent performance to treat the real samples. Moreover, the porous ZnO nano-crystal photocatalyst could easily be recycled without notable loss of catalysis ability.

Interaction study of collagen and sericin in blending solution.

The interactions of collagen and sericin were studied by fluorescence spectra, ultraviolet spectra, FTIR spectra and dynamic light scattering. The fluorescence quenching in emission spectra and red-shift (283-330nm) in synchronous fluorescence spectra suggested the Tyr of collagen and sericin overlapped with a distance of 3Å, generating excimer. The overlapped Tyr of collagen and sericin decreased the hydrophobicity of collagen, which resulted in the red-shifts (233-240nm) in ultraviolet spectra. Moreover, the red-shifts of amide bands of collagen in FTIR spectra indicated the hydrogen bonds of collagen were weaken and it could also be explained by the overlapped Tyr. The results of 2D-FTIR spectra demonstrated the backbone of collagen molecule was varied and the most susceptible structure of collagen was the triple helix with the presence of sericin. Based on dynamic light scattering, we conjectured large pure collagen aggregates were replaced by hybrid aggregates of collagen and sericin particles after the addition of sericin. With ascending sericin ratio, the diameters of the hybrid aggregates increased and attained maximum with 60% ratio of sericin, which were on account of the increasing excimer number. The results of DSC demonstrated the presence of sericin enhanced the thermal stability of collagen.