Synthesis and characterization of novel phenolphthalein immobilized halochromic fiber

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Dual pH/thermal-dependent coloring polymeric dye through Mannich reaction of chitosan: Synthesis and characterization

A novel polymeric dye was synthesized by one-pot Mannich reaction of chitosan (CS) and phenolphthalein (PHP). The grafting onto side chain of CS derivatives was confirmed by UV-vis, FT-IR, ¹H NMR techniques. The degree of substitution (DS) calculated by ¹H NMR and elemental analysis was revealed to increase with increasing mole ratio of formaldehyde and PHP. XRD analysis showed that the grafting through Mannich reaction was caused to amorphous structure in the derivatives. Covalent grafting of PHP onto CS made the grafted products showing pink color in basic conditions without leaching of dye and color fading after several weeks. Moreover, the derivatives dissolved in LiOH/urea systems could showed darker pink after heating. The results suggested that the novel CS derivatives with dual pH/thermal-dependent coloring property could potentially be prepared as pH/thermal-responsive biomaterial in a wide range of applications.

Highly selective and efficient chelating fiber functionalized by bis(2-pyridylmethyl)amino group for heavy metal ions

A classical bis(2-pyridylmethyl)amino group-modified polyacrylonitrile fiber possesses high selectivity and excellent recyclability for heavy metal ion absorption.

Adsorption of anionic MO or cationic MB from MO/MB mixture using polyacrylonitrile fiber hydrothermally treated with hyperbranched polyethylenimine

One-step hydrothermal treatment of polyacrylonitrile fiber (PANF) with hyperbranched polyethylenimine (HPEI) resulted in zwitterionic PANF-g-HPEI that contained not only the grafted HPEI moieties but also many COOH groups generated in situ. Increasing the weight gain of PANF-g-HPEI from 10% to 90% resulted in the increase of its COOH, amino and amide groups from 0.12 to 1.86 mmol/g, 1.44 to 8.90 mmol/g, and 0.67 to 2.12 mmol/g, respectively. Dye adsorption experiments demonstrated that (1) such PANF-g-HPEIs could effectively adsorb anionic Methyl Orange (MO) or cationic Methylene Blue (MB), through the pretreatment with acidic or basic solution, respectively; (2) PANF-g-HPEIs could selectively adsorb the anionic MO or the cationic MB from MO/MB mixture through the pretreatment with solution of pH=5 or 10, respectively; (3) the cationic or anionic dyes adsorbed by PANF-g-HPEIs could be reversibly desorbed by the aqueous solution of pH=1 or 10, respectively; (4) PANF-g-HPEI could be recycled efficiently, and its dye adsorption performances did not show pronounced loss even after 10 adsorption/desorption cycles, superior to PANF treated with the low molar-mass polyamines.

PAR immobilized colorimetric fiber for heavy metal ion detection and adsorption

A new wearable colorimetric fiber for heavy metal ion detection and adsorption has been synthesized by first aminating a commercially available polyacrylonitrile fiber with ethylenediamine and then covalently immobilizing 4-(2-pyridylazo)-1,3-benzenediol (PAR) on the modified fiber through a Mannich reaction. The fiber was characterized by X-ray powder diffraction spectra (XRD), scanning electron microscope (SEM), FTIR and UV-vis spectroscopy, and its acid exchange capacity, colorimetric properties, response speed, selectivity, reusability, photostability and adsorption capacity were investigated. In neutral aqueous solutions, the PAR immobilized fiber responds selectively to heavy metal ions, such as Hg(2+), Pb(2+), Cd(2+), Zn(2+), Ni(2+) and Cu(2+) with a color change from red-orange to dark-brown. Its visual detection limit for Pb(2+) is 1 x 10(-6)mol/L. Moreover, the selectivity increases with a decrease in pH, i.e. at pH 3.0, it shows a color change only for Hg(2+) and Cu(2+). This fiber also shows excellent reusability (>50 times), high photostability (>30 days under direct exposure to sunlight) and high adsorption capacity for Hg(2+) (0.74 mmol/g).