Typical conversion of lignocellulosic biomass into reducing sugars using dilute acid hydrolysis and alkaline pretreatment

The development and production of fossil fuel alternatives have become one of the main focal points in recent investigations. Lignocellulosic biomass is a renewable source of fermentable sugars for second-generation biofuels and chemicals via biotechnological pathways. However, the presence of lignin and hemicellulose in lignocellulosic biomass makes it difficult for the biomass to be hydrolyzed or digested during fermentation. Thus, effective biomass pretreatment is vital. The present review shows that chemical pretreatment is the current preferred method to obtain high sugar yields at low cost, with dilute acid and alkaline hydrolysis as the two most reported technologies. Dilute acid favours hydrolysis of the hemicelluloses whereas alkaline hydrolysis targets the lignin fraction. Both methods have merits and demerits, and have been combined with other treatments such as hydrothermal and enzymatic hydrolysis. Further investigation is required to improve the pretreatment processes and to ensure the economic viability of bioconversion.     

Synthesis and characterization of sol–gel alumina nanofibers

Abstract Alumina nanofibers of high aspect ratio with surface area of >300 m² g⁻¹ has been prepared successfully in bulk quantities by the sol–gel method. The synthesis parameters including the binary water–alcohol solvent system to aluminium isopropoxide ratio, pH, type of solvent and aging temperature affect the uniformity and formation of nanofibers. It is proposed that alumina nanofibers were formed by the curling of the nanosheets upon condensation after the hydrolysis. The phase evolution of alumina nanofibers from pseudoboehmite to α phase has been shown by XRD and FTIR. ²⁷Al NMR investigations show that the Al atoms are six and four coordinated. The morphology of the alumina nanofibers does not change much as the calcination temperature was increased. In addition, the average pore size increases and the BET surface area decreases as a function of calcination temperature. The thermal behavior of alumina nanofibers was investigated by TGA. Graphical Abstract      

Preparation and characterization of nanocrystalline Ca-doped CeO2 by sol–gel process

The reactivity of CeO₂ is determined by grain size and oxygen vacancies, which can be achieved by doping elements with less oxidation state into CeO₂. In this study nanocrystalline Ca-doped CeO₂ sol was synthesized from the reaction of hydrate cerium (III) nitrate and calcium nitrate tetrahydrate in alcohol solution after being calcined at 600?°C. X-ray diffraction as well as selected area electron diffraction gave evidence that the synthesized Ca-doped CeO₂ samples were well crystalline and had a cubic fluorite structure. TEM observation revealed that Ca-doped CeO₂ was composed by nanoparticles with grain size around 8?nm. The Raman spectrum of pure CeO₂ consists of a single triple degenerate F_2g model characteristic of the fluorite-like structure. In the Ca-doped CeO₂ sample, two additional low-intensity Raman bands were detected, thus confirming the formation of the solid solution. The synthesized nanometric powder is expected to be used in solid oxide fuel cells as well as in the catalytic treatment of automobile exhaust fumes.     

Phytochemical investigation of Gynura bicolor leaves and cytotoxicity evaluation of the chemical constituents against HCT 116 cells

Gynura bicolor (Compositae) is a popular vegetable in Asia and believed to confer a wide range of benefits including anti-cancer. Our previous findings showed that the ethyl acetate extract of G. bicolor possessed cytotoxicity and induced apoptotic and necrotic cell death in human colon carcinoma cells (HCT 116). A combination of column chromatography had been used to purify chemical constituents from the ethyl acetate and water extract of G. bicolor leaves. Eight chemical constituents 5-p-trans-coumaroylquinic acid (I), 4-hydroxybenzoic acid (II), rutin (III), kampferol-3-O-rutinoside (IV), 3,5-dicaffeoylquinic acid (V), kampferol-3-O-glucoside (VI), guanosine (VII) and chlorogenic acid (VIII) were isolated from G. bicolor grown in Malaysia. To our best knowledge, all chemical constituents were isolated for the first time from G. bicolor leaves except rutin (III). 3,5-dicaffeoylquinic acid (V), guanosine (VII) and chlorogenic acid (VIII) demonstrated selective cytotoxicity (selective index>3) against HCT 116 cancer cells compared to CCD-18Co human normal colon cells.     

Selective visible light reduction of carbon dioxide over iridium(III)-terpyridine photocatalysts

The CO₂ reduction reaction is an imperative piece of technology that closes the carbon cycle in many critical energy conversion and chemical manufacturing processes. Here, we report two new iridium (III) terpyridine-based photocatalysts capable of selective reduction of CO₂ to CO under visible light (λ ≥ 420 nm). The first photocatalyst, [Ir–COOH], was functionalized with the carboxyl group on the phenylpyridine, whereas the second, [Ir-PhCOOH], was attached to a phenyl spacer on the terpyridine. The [Ir-PhCOOH] was characterized by a higher extinction coefficient than [Ir–COOH], thus allowing more absorption of photons. Although both photocatalysts require two-electron activation, the [Ir-PhCOOH] is more readily activated as a result of the more negatively charged Ir center. These photocatalysts show exclusive selectivities in the production of CO. The turnover frequencies for [Ir–COOH] and [Ir-PhCOOH] were 19 and 10 h^?1, respectively, under visible light irradiation. The e-e-H-H pathway was identified as the most favorable, consisting of the rate-limiting step in the conversion of 1COOH to 1CO, and where the barrier is significantly lower for [Ir-PhCOOH] than for [Ir–COOH].     

Electrical conductivity of pyrolyzed polyacrylonitrile

Abstract

Using ultrapure samples of polyacrylonitrile (PAN) of 485,000 or 150,000 average molecular weight solution cast in dimethylformamide, the dc conductivity ([sgrave]) of pyrolyzed PAN (PANP) films has been studied for pyrolysis temperatures (T_p) of 280-435°C. Conductivity measurements made during pyrolysis indicate the onset of a dramatic increase in [sgrave] for T_p of 390-435°C. Conductivities as high as 5 (ohm-cm)^?1 have been observed for T_p < 435°C. This situation contrasts sharply with previous literature which had indicated that a increased uniformly and monotonically with T_p for 200°C < T_p < 900°C and that values of [sgrave] > 1 (ohm-cm)^?1 were observed only for T_p > 600°C. Our results indicate that the maximum value of [sgrave] obtained is not a strong function of T_p (390°C < T_p < 435°C) or of molecular weight. However, the rate of increase of [sgrave](t) is strongly dependent on T_p in this range. After pyrolysis, repeated heating and cooling below T_p do not alter [sgrave](T). IR spectra show that the sudden increase in [sgrave] is correlated to the formation of conjugated C=C and C=N bonds. The shape of [sgrave](T) suggests that conduction is probably due to hopping.