Starch-Mediated Immobilization, Photochemical Reduction, and Gas Sensitivity of Graphene Oxide Films.

This work unveils the roles played by potato starch (ST) in the immobilization, photochemical reduction, and gas sensitivity of graphene oxide (GO) films. The ST/GO films are assembled layer by layer (LbL) onto quartz substrates by establishing mutual hydrogen bonds that drive a stepwise film growth, with equal amounts of materials being adsorbed in each deposition cycle. Afterward, the films are photochemically reduced with UV irradiation (254 nm), following a first-order kinetics that proceeds much faster when GO is assembled along with ST instead of a nonoxygenated polyelectrolyte, namely, poly(diallyl dimethylammonium) hydrochloride (PDAC). Finally, the gas-sensing performance of ST/reduced graphene oxide (RGO) and PDAC/RGO sensors fabricated via LbL atop of gold interdigitated microelectrodes is evaluated at different relative humidity levels and in different concentrations of ammonia, ethanol, and acetone. In comparison to the PDAC/RGO sensor, the ones containing ST are much more sensitive, especially when operating in a high-relative-humidity environment. An array comprising these chemical sensors provides unique electrical fingerprints for each of the investigated analytes and is capable of discriminating and quantifying them in a wide range of concentrations, from 10 to 1000 ppm.

Corrigendum to "Preparation of PLA blends by polycondensation of D,L-lactic acid using supported 12-tungstophosphoric acid as a heterogeneous catalyst" [Heliyon 5 (5) (May 2019) e01810].

[This corrects the article DOI: 10.1016/j.heliyon.2019.e01810.].

Preparation of PLA blends by polycondensation of D,L-lactic acid using supported 12-tungstophosphoric acid as a heterogeneous catalyst.

Poly(lactic acid) (PLA) is a significant polymer that is based on renewable biomass resources. The production of PLA by polycondensation using heterogeneous catalysis is a focus for sustainable and economical processes. A series of samples comprising 12-tungstophosphoric acid (H3PW) supported on activated carbon, silica, and alumina induced the catalytic polymerization of D,L-lactic acid to form blends of PLA. The catalysts were characterized by multiple techniques to confirm the integrity of the Keggin anion as well as the acidity, which is the key property for relating structure to activity. The best reaction conditions were established for H3PW/C and tested for the other supported catalysts. The obtained polymer was a blend that was characterized as an enantiomeric excess (ee) of as much as 95% L-PLA (PLLA) with a mass average molar mass (M w ) of approximately 14,900 daltons. The role of H3PW in these polymerizations was demonstrated, i.e., without the Keggin acid, only oligomeric units (M w < 10,000 daltons) could be obtained. Additionally, inverse relationships between the M w of PLA and the enthalpy (-ΔH) of the strongest sites of the catalysts were distinguished, i.e., PLAMw-H3PW/C > PLAMw-H3PW/Al2O3 > PLAMw-H3PW/SiO2, whereas the acidity (-ΔH) order was as follows: H3PW/SiO2 > H3PW/Al2O3 > H3PW/C. These findings could be attributed to the correct tuning of strength and the accessibility of the sites to produce longer polymeric chains.

Quenching Effects of Graphene Oxides on the Fluorescence Emission and Reactive Oxygen Species Generation of Chloroaluminum Phthalocyanine.

The photophysical behavior and reactive oxygen species (ROS) generation by chloroaluminum phthalocyanine (AlClPc) are evaluated by steady state absorption/emission, transient emission, and electron paramagnetic resonance spectroscopies in the presence of graphene oxide (GO), reduced graphene oxide (RGO), and carboxylated nanographene oxide (NGO). AlClPc and graphene oxides form a supramolecular structure stabilized by π-π interactions, which quantitatively quenches fluorescence emission and suppresses ROS generation. These effects occur even when graphenes are previously functionalized with Pluronic F-127. A small part of quenching is due to an inner filter effect, in which graphene oxides compete with AlClPc for light absorption. Nonetheless, most of the (static) quenching arises on the formation of a nonemissive ground state complex between AlClPc and graphene oxides. The efficiency of graphene oxides on the fluorescence quenching and ROS generation suppression follows the order: GO < NGO < RGO.

Photochemically-assisted synthesis of non-toxic and biocompatible gold nanoparticles.

This contribution describes the photochemically-assisted synthesis of aqueous colloidal suspensions of non-toxic and biocompatible spherical gold nanoparticles stabilized by branched polyethylenimine, or else Au-np-PEI. The method consists on 30min of photoexcitation (254nm, 16W) at room temperature of an aqueous diluted solution of chloroauric acid (HAuCl4) containing PEI. While the UV irradiation forms the [Au(3+)Cl4-]* excited species that succesively transforms into zero valent Au, PEI controls the nucleation step of nanoparticles formation. Varying the PEI to Au molar ratio permits one to tune the size of nanoparticles between 100nm to 8nm. The obtained colloidal suspensions display an intense plasmonic absorption band at 520-530nm and positive zeta potentials greater than +20mV. The cells viability for in vitro tests performed with human connective tissues and human breast adenocarcinoma (MCF-7) cell lines is over 80% and 90%, respectively, when they are incubated with Au-np-PEI formulations (25µgmL-1). The present photochemically-assisted synthesis is advantageous because it is fast and does not require for either hazardous or cytotoxic reductant agents and additional purification procedures.