Font Size: a A A

Construction And Catalytic Performance Of Micro Fluidic System Based On PECVD Method

Posted on:2017-01-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:X RaoFull Text:PDF
GTID:1221330488957742Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
Recently, the research on micro fluidic system is attractive in chemical synthesis area. It is interesting to build the micro fluidic systems based on microreactors and consequently use them for high efficiency heterogeneous catalytic reaction. In this work, firstly three related aspects are systematically investigated:(1) amine functionalization on various substrate surfaces using plasma enhanced chemical vapor deposition (PECVD) method; (2) synthesis of gold nanoparticles (AuNPs) and their immobilization on substrate surface; (3) immobilization of AuNPs on zeolites and their deposition on substrate surface. Thereafter, the microreactors are made from cyclic olefin copolymer (COC), their inner channel surface are functionalized with amine using PECVD method; meanwhile, the catalysts (AuNPs and AuNPs@zeolite) are prepared and silanized; then the catalysts particles are fixed upon the surface through electrostatic interaction to make catalytic microreactors. Finally, the microreactors are connected into the pre-designed micro fluidic system. The catalytic performance of the system is investigated through benzyl alcohol oxidation reaction in water medium.The results show that PECVD method is a universal method that could deposit high amine content of (3-aminopropyl)triethoxysilane (APTES) polymerized film on various substrate surfaces. Ar and N2 are good active gas for APTES plasma polymerization; however, O2 is not appropriate as it leads to over oxidation of APTES and formation of SiO2 like structures during deposition process. In order to obtain good deposition and diminish the functional change due to coating being exposed to plasma, the deposition time should be in the range of 14-40s. Furthermore, the investigation of APTES deposited using different working pressure indicates the competition between fragmentation and/or poly-recombination of the APTES molecules and normal ionic or/and radical polymerization determines the coating chemical composition and functional groups. Moreover, the coating stability increases when the power is increased between 25-40W, indicating a high cross-linked structure due to higher plasma power; however, the intensity of fragmentation of APTES is also enhanced with increasing power, if the power is too high the amine functions are lost during fragmentation. The comparison of amine proportion of total composition and coating stability in this study indicates optimization plasma conditions for APTES deposition:Qaptes= 10sccm, QAr=20sccm, P=30W, p=1.0mbar, t=40s.Compared with conventional wetchemistry method, PECVD polymerized APTES coating exhibits better hydrophilicity, higher coating thickness, as well as higher amine groups density, leading to a further higher coverage and amount of AuNPs. During immobilization process, the pH value 6.2 of colloidal solution leads to transformation of high amount protonated amines on substrate surface. After gold immobilization, the content of protonated amine groups increase as well as its XPS peak center shifts towards to lower binding energy, evidencing AuNPs are successfully immobilized through binding to R-NH3+ species.The comparison study of using APTES and MPTES for surface modification and then immobilizing AuNPs on Y type zeolite, indicates the APTES is a better linker as it provides higher amount of gold loading at the same condition. For zeolite and AuNPs@zeolite deposition, the particles are functionalized with carboxyl group using CES as a linker for bounding the protonated amines on COC surface that is pre-modified using PECVD method. Concerning pKaNH2 of 10.6 and pKacooH of 2.5, the pH value of 8.4 is used for obtaining more free carboxylic acid. A complete and even coverage of zeolite and AuNPs@zeolite deposition over the entire COC substrate surfaces are observed. The coating is fairly stable in hydrodynamic flows and could be further used in microfluidics.The gold type\Y zeolite type\AuNPs@zeolite type microreactors are respectively connected into pre-designed micro fluidic system. Their catalytic performances on transforming benzyl alcohol to benzaldehyde are investigated in water medium. The gold type microreactor exhibits stable high selectivity to benzaldehyde (about 94%), however it also shows relative low benzyl alcohol conversion (about 20%). The Y-zeolites are evidenced to be not a catalytic active phase in our system, they only exhibit benzyl alcohol absorption ability as they are used in the microchannel. Moreover, the AuNPs@zeolites type microreactor performs the best catalytic activity in our study, the higher benzyldehyde selectivity (>99%) are obtained with the highest benzyl alcohol conversion (about 40%). Finally, the absorption-catalysis mode of benzyl alcohol in AuNPs-zeolite system is successfully built up.
Keywords/Search Tags:Microfluidics, Gold nanoparticles, Y type zeolite, Plasma enhanced chemical vapor deposition(PECVD), Catalytic performance
PDF Full Text Request
Related items