RESUMEN
CdS nanoparticles have wide applications as photocatalysts for degradation of organic pollutants, but due to their limited turnover number and off-pathway charge recombination processes, their degradation efficiency is low. Herein, aminated graphene quantum dots/CdS (GQDs/CdS) nanobelts were successfully fabricated by solvothermal and hydrothermal processes. The prepared GQDs/CdS were characterized by physical methods to investigate their structure, morphology, optical properties, specific surface area, element composition, and chemical state. GQDs/CdS materials promoted efficient charge separation, and showed high efficiency in the photocatalytic degradation of the organic dye Rhodamine B (RhB) under visible light. The degradation efficiency of RhB samples over 0.05 g of catalysts reached 97.40% after 150 min, a much higher efficiency in comparison to pure CdS. Electron paramagnetic resonance (EPR) spectroscopy provided direct evidence for ËOH and ËO2- as the reactive oxidative species using DMPO as a spin trap. Consistent with the experimental results, a possible mechanism of RhB photocatalytic degradation by GQDs/CdS under visible light was proposed. This work may provide environmentally friendly photocatalysts for degrading organic dyes and purifying water.
RESUMEN
Strontium titanate (SrTiO3) is considered to be a promising photocatalyst. However, the rapid recombination of photo-generated charge carriers limits the practical applications of SrTiO3-based photocatalysts. In this work, we prepared hydrogenated SrTiO3 using NaBH4 as a reducing reagent. The optimized photocatalyst shows a H2-evolution rate up to 409.5 µmol g-1 h-1 with a CuS co-catalyst, which is 152, 14 and 1.8 times higher than those of pure SrTiO3, hydrogenated SrTiO3, and CuS/SrTiO3, respectively. The enhanced photocatalytic H2-evolution activity can be attributed to the synergistic effect of the CuS co-catalyst and the appropriate oxygen vacancies produced by hydrogenation, which are beneficial for lowering the separation of photo-generated charge carriers. The present finding could shed light on the design of efficient SrTiO3-based photocatalysts.
RESUMEN
We used molecular dynamics (MD) simulation to study the diffusion of water at low concentrations in a series of chemically modified xylans, a major hemicellulose, including hydroxypropyl xylan (HPX) and acetoxypropyl xylan (APX) which is essentially acetylated HPX, with different degrees of acetylation (i.e., different degrees of hydrophobicity) at 400 K, a temperature well above the glass transition temperatures of the materials. We used one HPX and three APX models. The three APX models were constructed using the HPX model by substituting 1, 2 or 3 hydroxyl moieties on its repeating units, respectively. The simulation results showed that the diffusivity of water at low concentrations in the chemically modified xylans decreased slightly (~20%) from HPX to APX with 3 acetylated hydroxyl moieties, a trend that has been experimentally observed for xylans and other cellulosic type materials. Further data analysis shows that acetylation decreases the ability of the xylan to form hydrogen bonds with water and its degree of swelling. And these two factors exert opposite effects on the diffusivity of water. In particular, the first factor increases the mobility (lower activation energy) of the water molecules, while the second factor reduces the free volumes available for diffusion, thereby decreasing the water mobility. This finding implies that it is not likely to obtain orders of magnitude change to the water diffusivity simply by the acetylation of all hydroxyl moieties on xylan. The high degree of swelling observed for HPX compared to those of APXs is attributed to the fact that many hydrogen bonds in HPX are broken by water. It is interesting to note that water in most of the hydrogen bonds formed between water and xylans acted as hydrogen bond acceptors rather than donors.