Highly dispersive PdCoB catalysts for dechlorination of chlorophenols

Synthesis of Pd-CoxOy Hybrid Nanostructure-Encapsulated Hollow Silica Nanospheres through Reverse Microemulsion Systems and Their Application as Efficient Hydrodechlorination Catalysts

Pd-Co_xO_y heteroaggregate-encapsulated hollow porous silica nanoreactors (Pd-Co_xO_y@HPSNs) were synthesized by a reverse microemulsion system. The key design of the developed reverse microemulsion system is to use poly(ethyleneimine) in the water droplets as the void templates for silica deposition and for anchoring the catalytic functionality inside the hollow silica nanospheres. The synthesized Pd-Co_xO_y@HPSNs contain ∼3 nm Pd-Co_xO_y hybrid nanostructures in ∼10 nm central cavities of silica nanospheres and illustrated a significantly promoted efficiency for hydrodechlorination of a series of chlorophenols into phenols under mild reaction conditions. The catalytic enhancement of Pd-Co_xO_y@HPSNs is ascribed to the synergistic effect between Pd and Co_xO_y and the protection of silica shells to the inner catalytic functionality.

Wood preservatives in children's wooden toys from China: Distribution, migration, oral exposure, and risk assessment

A total of 90 wooden toys were collected, and six wood preservatives (chlorophenols and lindane) were analyzed by using gas chromatography-tandem mass spectrometry to assess the exposure risk of children to wood preservatives through oral contact with wooden toys. The detection rates of six preservatives ranged from 2.2% to 22.2%. The contents of the preservatives ranged from 0.6 µg/kg to 9.6 µg/kg. 2,4-Dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) had higher detection rates and contents than other preservatives. Thus, their migration behaviors from toys to saliva were further investigated. In 11 positive samples, the max migration ratios of 2,4-DCP and 2,4,6-TCP ranged from 7.1% to 20.3% and from 11.1% to 24.8%, respectively. For children aged 3-36 months, the daily average 2,4-DCP exposure level associated with wooden toys ranged from 2.7 pg/(kg day) to 46.9 pg/(kg day), and the daily average 2,4,6-TCP exposure ranged from 3.6 pg/(kg day) to 69.4 pg/(kg day). The contribution to exposure provided by the saliva mobilization pathway was more than that provided by the ingestion of scraped-off toys, and the exposure level of 2,4,6-TCP was greater than that of 2,4-DCP. The max hazard quotient for 2,4-DCP was 1.9 × 10^-4, and the max cancer risk for 2,4,6-TCP was 1.2 × 10^-9. The above results indicated that although wood preservatives were distributed in wooden toys, exposure arising from directly mouthing these materials currently does not pose unacceptable risks to children.

Migration regularity of six preservatives from wooden children's products to saliva and sweat based on microstructure-related migration models

Wood preservatives in wooden children's products (WCPs) may migrate into children's body through oral and dermal exposure, resulting in a potential health risk. In this paper, a systematic investigation on the migration regularity of lindane and five chlorophenols preservatives from WCPs to saliva and sweat was introduced. Migration models were established based on the abundant migration data among different time periods (2 min-96 h). Wood exhibited complex porosity for various species, resulting in the deviation of the migration of preservatives from different samples. By introducing a correction coefficient (f) calculated based on the sample microstructure (specific surface area and pore distribution), the predicted values of correcting migration model matched better with the experimental data. Migration data indicated that exposure risks should be noticed when children were in contact with WCPs because a considerable quantity of preservatives migrated into the body in a short time. This work is expected to play a role in the formulation of chemical limit standards to promote the safety of WCPs, and may serve ideas as basis for the migration research of chemicals in wooden products.

Catalytic hydrodechlorination of triclosan using a new class of anion-exchange-resin supported palladium catalysts

We prepared a new class of anion-exchange-resin supported Pd catalysts for efficient hydrodechlorination of triclosan in water. The catalysts were prepared through an initial ion-exchange uptake of PdCl₄^2- and subsequent reduction of Pd(II) to Pd(0) nanoparticles at ambient temperature. Two standard strong-base anion exchange resins (IRA-900 and IRA-958) with different matrices (polystyrene and polyacrylic) were chosen as the supports. SEM and TEM images showed that Pd(0) nanoparticles were evenly attached on the resin surface with a mean size of 3-5 nm. The resin supported Pd catalysts (Pd@IRA-900 and Pd@IRA-958) were able to facilitate rapid and complete hydrodechlorination of triclosan. At a Pd loading of 2.0 wt.%, the observed pseudo first-order rate constant (k_obs) was 1.25 ± 0.06 and 1.6 ± 0.1 L/g/min for Pd@IRA-900 and Pd@IRA-958, respectively. The catalysts were more resistant to Cl^- poisoning and natural organic matter fouling than other supported-Pd catalysts. The presence of 10 mM NaCl suppressed the k_obs value by 31% and 23% for Pd@IRA-900 and Pd@IRA-958, whereas the presence of humic acid at 30 mg/L as TOC lowered the rates by 28% and 27%, respectively. The better performance of Pd@IRA-958 was attributed to the polymeric matrix properties (i.e., hydrophobicity, pore size, and surface area) as well as Pd particle size. GC/MS analyses indicated that very low concentrations of chlorinated intermediates were detected in the early stage of the hydrodechlorination process, with 2-phenoxyphenol being the main byproduct. The catalysts can be repeatedly used in multiple operations without significant bleeding. The catalysts eliminate the need for calcination in preparing conventional supported catalysts, and the resin supports conveniently facilitate control of Pd loading and material properties.