Chenxi Zhang

Preparation of compound coating of fluorine conversion layer and calcium phosphate on AZ31 magnesium alloy

Abstract A compound coating with MgF2 layer in the inner region and flaky Brushite (DCPD) crystal layer in the outer region was prepared on AZ31 alloy to improve the corrosion resistance and osteoconduction of magnesium alloys in simulated body fluids. Hydrogen evolution test and potentiodynamic electrochemical technique were employed to investigate the corrosion behaviour of the coated alloys in Hank’s solution. The obvious decrease in corrosion current density and hydrogen evolution rates indicate that both MgF2 layer and DCPD/MgF2 compound coating could enhance the corrosion resistance of the substrate. DCPD on MgF2 layer increases the Ecorr and Ebk of the MgF2 coated sample and decreases the corrosion current density. Moreover, the hydrogen volume of the DCPD/MgF2 coated sample is much less than that of the MgF2 coated sample in the first week’s immersion, which indicates that DCPD can delay the degradation of MgF2 and postpone the corrosion of AZ31 alloy in Hank’s solution.

Preparation of palladium nanoparticles supported on conjugated microporous polymers with excellent catalytic performance

Conjugated microporous polymers (CMPs) are a class of microporous organic polymers that consist with most conjugated π-systems. In this work, CMPs with high surface area of 1082 m2 g− 1 and pore volume were synthesised. Using H2PdCl4 as metal precursor, NaBH4 aqueous solution as reducing agent and the as-synthesised CMPs as catalyst supports, Pd@CMP-1 catalyst was successfully prepared. Hydrogenation reaction of 4-Nitrotoluene was employed as a probe reaction to investigate the catalytic performance of Pd@CMP-1 catalyst. The palladium nanoparticles can be well dispersed and loaded on the CMPs to afford an efficient catalyst by immersion and reduction method. Also, the synthesised catalyst possessed high activity and selectivity. Moreover, different percentages of palladium and pressure nearly have little influences on the reactions and the catalyst had certain cycle performance after five times by simple centrifugation, suggesting that the Pd@CMP-1 catalyst had certain chemical stability. The high catalytic performance has been attributed to the special structure of CMPs. This work might provide useful guidance for rational design and preparation of novel CMPs–metal nanoparticles catalysts for various catalytic reactions by loading different metal nanoparticles on various CMPs.