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The reaction of ground state NH with H2 has been studied in a high-temperature photochemistry (HTP) reactor. The NH (X 3 Σ) radicals were generated by the 2-photon 193 nm photolysis of NH3, following the decay of the originally produced NH(A 3 Π) radicals. Laserinduced fluorescence on the NH(A 3 Π-X 3 Σ 0,0) transition at 336 nm was used to monitor the progress of the reaction. We obtained k (833-1432 K) = 3. showing the barriers leading to these products to be too high compared to the measured activation energies. The calculations indicate the likelihood of formation of adducts, of low stability. These then may undergo further reactions. The NH + H2O reaction is briefly discussed and it is similarly argued that HNO + H2 cannot be the products, as had been previously suggested.3

Chitosan is a biodegradable polymer composed of randomly distributed β‐(1,4)‐linked D‐glucosamine (deacetylated unit) and N‐acetyl‐D‐glucosamine (acetylated unit). It is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans (such as crabs and shrimps) and the cell walls of fungi. In the work reported, we developed a facile technique for the preparation of chitosan by irradiating prawn shell at various intensities from 2 to 50 kGy. It was observed that γ‐irradiation of prawn shell increased the degree of deacetylation (DD) of chitin at a relatively low alkali concentration during the deacetylation process. Among the various irradiation doses applied to prawn shell, a dose of 50 kGy and 4 h heating in 50% NaOH solution yielded 84.56% DD while the chitosan obtained from non‐irradiated prawn shell with the same reaction conditions had only 74.70% DD. In order to evaluate the effect of γ‐irradiation on the various physicochemical, thermomechanical and morphological properties, the chitosan samples were again irradiated (2–100 kGy) with γ‐radiation. Molecular weight, DD, thermal properties with differential scanning calorimetry and thermogravimetric analysis, particle morphology by scanning electron microscopy, water binding capacity (WBC), fat binding capacity (FBC) and antimicrobial activity were determined and the effects of various γ‐radiation doses were assessed. The DD, WBC, FBC and antimicrobial activity of the chitosan were found to improve on irradiation. It was obvious that irradiation caused a decrease of molecular weight from 187 128 to 64 972 g mol−1 after applying a radiation dose of 100 kGy which occurred due to the chain scission of chitosan molecules at glycosidic linkages. The decrease of molecular weight increased the water solubility of the chitosan, the extent of which was explored for biomedical applications. Copyright © 2012 Society of Chemical Industry

Nitrogen-doped carbon catalysts prepared from amino-functionalized metal–organic frameworks [amino-MIL-101­(Al)] were investigated for the oxygen-reduction reaction (ORR) with special emphasis on elucidating the role of different nitrogen species (e.g., pyridinic, pyrrolic, and quaternary N) as active catalytic sites. Careful optimization of pyrolysis temperature of the amino-MIL-101­(Al) leveraged the synthesis of the catalysts with or without quaternary N functionalities. This allowed us to investigate the type(s) of N species responsible for the ORR catalysis and thus address the conflicting results reported so far regarding the pyridinic and/or quaternary N as active sites for ORR catalysis via four-electron transfer (4e–) pathways. Our findings suggest that the total nitrogen content in the catalysts does not influence the ORR, while the quaternary N sites exclusively catalyze the reduction of O2 via the 4e– transfer pathway in both alkaline and acidic electrolytes. Catalysts containing only pyridinic and pyrrolic N were observed to be ineffective for the ORR. The experimental results were further supported by computational simulation using the gradient–correlated density functional theory which revealed that the dissociative O2 adsorption (i.e., binding and cleavage of OO bonds) is more favorable to quaternary N. Furthermore, calculations based on the relative surface potential energy, dipole moment, binding energy, and electron density indicate that the most stable structure of O2 chemisorption sites could only be achieved on the quaternary N carbon.

Activated carbon/titanium dioxide (AC/TiO2) nanohybrids were synthesized by a hydrothermal technique using various weight percent of commercial AC and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The synthesized nanohybrids were applied to photodegradation of Reactive Red-35 (RR-35) dye in aqueous solution using sunlight. Due to the synergistic effect of adsorption and photodegradation activity, AC/TiO2 nanohybrids were more efficient in treating the aqueous dye solution than that of AC and TiO2. The maximum (95%) RR-35 dye removal from the water was obtained with 20 wt% AC/TiO2 within 30 min at natural pH of 5.6. The possible photodegradation mechanism of RR-35 dye with AC/TiO2 was discussed from the scavenger test. Moreover, AC/TiO2 was found to be suitable for long-term repeated applications through recyclability experiments. Therefore, AC/TiO2 nanohybrid is a promising photocatalyst for treating azo dyes especially RR-35 from water.

Abstract. Functionalization of indigenous materials improves inherent physicochemical properties that depend mainly on their fabrication techniques. Here, pH triggered biocomposites using different proportions of kaolinite and chitosan were fabricated. It was revealed that the biocomposites were formed in 1M acetic acid and stabilized after dropwise addition of the mixture of kaolinite and chitosan solution in 3M NaOH. Binding of kaolinite and chitosan at their interface through functional groups was studied using Fourier transform infrared (FT-IR) spectroscopy and dynamic light scattering (DLS). The average particle size of the biocomposite in aqueous system having 80% w/w kaolinite and 20% w/w chitosan was determined to be 400.8 nm. Crystallinity disappearance of chitosan in the biocomposite, as shown in x-ray diffraction (XRD) spectrum, supports the wrapping of kaolinite with soft and flexible chitosan. Differential scanning calorimetry (DSC) showed the thermal stability of the biocomposites and it was found that the biocomposite fabricated from 50% w/w kaolinite and 50% w/w chitosan was stabled up to 318 o C. Morphological studies were carried out using scanning electron microscopy (SEM), where a progressive tendency towards granular morphology was evidenced with increase in kaolinite content. These functionalized materials in bionanocomposite structure would play a vital role in advanced research in analytical and environmental science.

Heavy-metal pollution of surface water, sediment and fish have been seen as a major global problem, with a significant proportion of developing countries like Bangladesh. This study assessed the intensity of alarming six toxic substances (Cr, Zn, Fe, Cu, Pb and Ni) throughout the River water, sediments as well as soft tissues of three widely consumed fishes (Heteropneustes fossilis, Channa punctatus and Channa striata) obtained from two urban streams of the Buriganga and Turag in the Dhaka metropolitan. For evaluating the comparative seasonal variation of heavy-metal concentration, water and sediment samples were collected from five selected sites for two different seasons (viz. 10 from winter seasons and 10 from summer seasons). Finally, a total of 20 water samples, 20 sediment and 12 fish samples were investigated by flame atomic absorption spectroscopy (FAAS) and graphite furnace atomic absorption spectrometer (GFAAS) corrected with the Zeeman effect background correction system. The hierarchy of mean concentration of selected heavy metals in Buriganga water is found to be Fe > Cr > Ni > Zn > Cu > Pb in the winter season whereas during the summer season the order is Fe > Cr > Zn > Ni > Cu > Pb. For the River Turag, the order is Fe > Zn > Cu > Ni > Cr > Pb and Fe > Zn > Ni > Cu > Cr > Pb during winter and summer season, respectively. The level of metals studied surpassed the acceptable level of drinkable water, implying the ineptitude of drinking and cooking water from these Rivers. However, this hierarchy of heavy metals for sediments of Buriganga River changed to Fe > Cr > Ni > Zn > Cu > Pb for the winter season and Fe > Cr > Ni > Cu > Zn > Pb for the summer season. Whereas, for the Turag River, the decreasing trend of metal concentration found in sediment was Fe > Zn > Cr > Ni > Cu > Pb for both seasons. For probable human health hazard implications, contamination factor (CF) and pollution load index (PLI) were studied. The CF values revealed the low-to-moderate pollution of sediment. The PLI value above one shows the degradation of the consistency of the sediments. Fe, Ni, Pb, Cr, Zn and Cu concentrations in fish species were found to be 19.66–45.1, 0.07–12.18, 1.2–10.18, 20.18–187.07, 11.08–68.25, 2.07–10.4 mg/kg, respectively. The metals studied differed considerably among organisms and seasons. Bioconcentration factor (BCF), the daily average consumption of metal (EDI), as well as target threat quotients (THQs) for specific metal indicated that Cr and Pb are harmful in fish muscles and possible risks remain for fish consumers. The obtained concentrations of some metals are higher than the WHO/FAO’s permissible limit, suggesting that the water and fish found in these Rivers are like to be harmful to the human being. This study shows that attention should be given to the risk assessment for heavy metals in these Rivers.

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