Efficient Cr(VI) removal from wastewater by D-(+)-xylose based adsorbent: Key roles of three-dimensional porous structures and oxygen groups.

Reducing the harm of heavy metals to the environment has been a major scientific challenge. In this study, D-(+)-xylose was used to prepare an adsorbent with rich O groups and three-dimensional porous structures for Cr(VI) adsorption. What's more, the adsorption sites of many oxygen groups in the material were combined with the three-dimensionally connected porous structures, which made the adsorption sites fully in contact with Cr(VI). At the concentration of 300 mg/L, the removal rate of Cr(VI) was 94.50%, 6.4 times that of the non-porous treatment and 9.6 times that of the non-porous and O group treatment. The adsorbent showed a high adsorption capacity (910.10 mg/g) for Cr(VI), and the adsorption model proved that the adsorbent was a multi-molecular layer adsorbent. In addition, the adsorption was controlled by chemical reaction and diffusion, which was also attributed to the three-dimensional porous structure and abundant oxygen groups of the material. XPS and FTIR indicated that four O groups participated in the adsorption reaction (-OH, C-O-C, CO, and C-O), and C-O-C and C-O were the main reaction sites. After treating wastewater from electroplating plants with X-PC, the discharged water met international and domestic discharge standards (Cr(VI) removal rate> 99.90%). This work provides a new idea for the application of sugars in the environment and the design of porous adsorbents.

Mesoporous LaCoO3 perovskite oxide with high catalytic performance for NOx storage and reduction.

A mesoporous LaCoO3 perovskite oxide (LaCoO3-Meso) with three-dimensionally ordered helical interwoven structure was synthesized by a nano-casting method using KIT-6 as the hard template. The obtained LaCoO3-Meso with high surface area was tested for its catalytic performance in the NOx storage and reduction (NSR) reaction and compared with a sample synthesized by the conventional sol-gel method. The LaCoO3-Meso showed a significant advantage for NOx storage, with a NOx storage capacity 2 times higher than the regular sample. LaCoO3-Meso also exhibited improved NSR catalytic performance in the 150-450 °C temperature range, especially within 350-400 °C, where the NOx conversion was raised for 40%. The results of X-ray photoelectron spectroscopy and X-ray absorption fine structure measurements suggested the presence of a high concentration of oxygen defects on the LaCoO3-Meso surface. Further results provided by temperature programmed reduction and temperature programmed desorption indicated that the oxygen defects not only increase the amount of trapped NOx, but also improve the low-temperature redox performance of the catalyst. The lower stability of NOx species adsorbed on oxygen defects promotes the NOx release step in the NSR reaction and benefits the regeneration of storage sites.

Polymerizable Microsphere-Induced High Mechanical Strength of Hydrogel Composed of Acrylamide.

Polymerizable microspheres are introduced into acrylamide to prepare the high mechanical strength hydrogels with a novel three-dimensional pore structure. Rheological properties, compressive stress⁻strain, tensile property, and compression strength of three different types of hydrogels were investigated. Moreover, a scanning electron microscope (SEM) was adopted to observe the three-dimension network structure of three different types of hydrogels. The test results illustrated that viscous moduli (G″) and elastic moduli (G') of a hydrogel containing polymerizable microspheres (P) reached maximum values, compared to the normal hydrogel (N) and the composite hydrogel containing ordinary microspheres (O). When the hydrogels were squeezed, the N was easily fractured under high strain (99%), whereas the P was not broken, and quickly recovered its initial morphology after the release of load. The P showed excellent tensile properties, with an elongation at break up to 90% and a tensile strength greater than 220 g. The compression strength of the N was 100.44 kPa·m-1, while the resulting strength of P was enhanced to be 248.00 kPa·m-1. Therefore, the various performances of N were improved by adding polymerizable microspheres. In addition, the SEM images indicated that N has a general three-dimensional network structure; the conventional network structure did not exist in the P, which has a novel three-dimensional pore structure in the spherical projection and very dense channels, which led to the compaction of the space between the three-dimensional pore network layers and reduced the flowing of free water wrapped in the network. Therefore, the mechanical strength of hydrogel was enhanced.