Rajangam Vinodh

Novel microporous hypercross-linked conjugated quinonoid chromophores with broad light absorption and CO2 sorption characteristics

We have discovered formation of hypercross-linked conjugated quinonoid chromophores (polymers) with broad light absorption characteristics during cross-linking of aromatic monomers, such as benzene, naphthalene, anthracene, phenanthrene and 1,3,5-trimethyl benzene with 1,3,5-trioxane in the presence of an FeCl3 catalyst. The para or ortho –CH2 groups that bridge aromatic monomers were dehydrogenated during polymerization to form the quinonoids. The quinonoid chromophores were confirmed by their DRS-UV Vis and FTIR spectra. We have also discovered similar such quinonoid chromophores in the hypercross-linked polymers of aromatic monomers, reported from 1970 onwards by different research groups. The polymers were synthesized by similar experiments with an FeCl3 catalyst, and brown colored. As all the polymers bear low band gaps, they strongly absorb light covering the wavelength range of 1000 to 200 nm. Most of the hypercross-linked polymer matrices carry microporous spheres of about 1 to 5 μm diameter and showed 6–7% CO2 sorption. The polymers with their low band gaps will inspire research on semiconductors, solar cell devices, UV stabilizers/absorbers and infrared absorbers/detectors, molecular sensors and academic study.

A new strategy to synthesize hypercross-linked conjugated polystyrene and its application towards CO2 sorption

Polystyrene is cross-linked to generate micropores for sorption applications. Herein, we report, hypercross-linking of polystyrene in the presence of Friedel-Crafts catalyst, FeCl3 without a cross-linker. For comparison, polystyrene was also hypercross-linked with a cross-linker, dimethoxy methane with the same catalyst. The cross-linking and de-hydrogenation of cross-links to quinonoid formation were confirmed by FT-IR and 13C-NMR techniques. The hyper cross-linked polymers (HCPs) were also characterized by TGA, DRS-UV, SEM, Raman, BET and CO2 sorption techniques. All the HCPs showed a maximum of 5 weight % CO2 sorption at 25 oC and 1 atm. The same polymers could also be applied for the sorption of other air pollutants.

Microporous Hypercross-linked Conjugated Quinonoid Chromophores of Anthracene: Novel Polymers for CO 2 Adsorption

Microporous hypercross-linked conjugated quinonoid chromophores represent a novel class of amorphous polymers, synthesized by the reaction of anthracene with dimethoxy methane in the presence of FeCl3 catalyst. Their N2 adsorption isotherms confirm their microporous nature. Diffuse reflectance UV-Visible (DRS UV-Vis) spectroscopy confirms their matrix built with the conjugated quinonoids by their broad light absorption characteristics extending from 1000 nm to 200 nm with the absorbance maximum close to 400 nm. The catalyst cross-linked anthracene with -CH2- bridges and subsequently dehydrogenating them to form quinonoids. Their Fourier transform infrared (FTIR) spectra showed their characteristic quinonoid vibrations between 1600 and 1700 cm−1. The synthesis of polymers was carried out at 30, 40, 50, 60, 70 and 80 °C, but the quinonoid content of the polymer obtained at 80 °C was higher than that of the others. Their scanning electron microscopy (SEM) images showed microspheres of 1 to 5 μm size built with tiny particles. Their surfaces were not smooth. The polymer synthesized at 80 °C showed 5.1 wt% CO2 sorption at 25 °C and 0.1 MPa, but when it was recross-linked, the CO2 sorption increased to 8 wt%. Hence, hypercross-linked conjugated quinonoid chromophores of anthracene are good for sorption of CO2.

An ultrasensitive photoelectrochemical biosensor for glucose based on bio-derived nitrogen-doped carbon sheets wrapped titanium dioxide nanoparticles

In this work, an ultra-sensing photoelectrochemical (PEC) glucose biosensor has been constructed from the bio-derived nitrogen-doped carbon sheets (NDC) wrapped titanium dioxide nanoparticles (NDC-TiO2 NPs) followed by the covalent immobilization of glucose oxidase (GODx) on them (designated as a GODx/NDC-TiO2NPs/ITO biosensor). Initially, the TiO2 NPs was synthesized by sol-gel method and then NDC-TiO2 NPs was synthesized utilizing a green source of Prunus persica (peach fruit) through a simple hydrothermal process. The synthesized NDC-TiO2 NPs composite was characterized by FESEM, HRTEM, Raman spectroscopy, XRD, ATR-FTIR spectroscopy and XPS to determine composition and phase purity. These fabricated GODx/NDC-TiO2NPs/ITO biosensor exhibited a good charge separation, highly enhanced and stable photocurrent responses with switching PEC behavior under the light (λ > 400 nm). As a result, GODx/NDC-TiO2NPs/ITO PEC glucose sensor exhibits a good photocurrent response to detection of glucose concentrations (0.05-10 μM) with an ultra-low detection limit of 13 nM under optimized PEC experimental conditions. Also, the PEC glucose sensor revealed a high selectivity, good stability, long time durability, and capability to analyze the glucose levels in real human serum. Also, the further development of this work may provide new insights into preparing other bio-derived carbon nanostructure-based photocatalysts for PEC applications.