Acid/Base Treatment of Monolithic Activated Carbon for Coating Silver with Tunable Morphology

Silver coatings on the exterior surface of monolithic activated carbon（MAC） with different morphology were prepared by directly immersing MAC into [Ag（NH3）2]NO3 solution. Acid and base treatments were employed to modify the surface oxygenic groups of MAC, respectively. The MACs＇ Brunauer-EmmettTeller（BET） surface area, surface groups, and silver coating morphology were characterized by N2 adsorption, elemental analysis（EA）, X-ray photoelectron spectroscopy（XPS）, and scanning electron microscopy（SEM）, respectively. The coating morphology was found to be closely related to the surface area and surface functional groups of MAC. For a raw MAC which contained a variety of oxygenic groups, HNO3 treatment enhanced the relative amount of highly oxidized groups such as carboxyl and carbonates, which disfavored the deposition of silver particles. By contrast, Na OH treatment significantly improved the amount of carbonyl groups, which in turn improved the deposition amount of silver. Importantly, lamella silver was produced on raw MAC while Na OH treatment resulted in granular particles because of the capping effect of carbonyl groups. At appropriate [Ag（NH3）2]NO3 concentrations, silver nanoparticles smaller than 100 nm were homogeneously dispersed on Na OH-treated MAC. The successful tuning of the size and morphology of silver coatings on MAC is promising for novel applications in air purification and for antibacterial or aesthetic purposes.

Enhanced photocatalytic performance of cementitious material with TiO_2@Ag modified fly ash micro-aggregates

A TiO2 photocatalyst is coated on the surface of a zeolite fly ash bead（ZFAB） to improve its dispersability and exposure degree in a cement system.The application of Ag particles in TiO2/ZFAB modified cementitious materials is to further enhance the photocatalytic performance.Various Ag@TiO2/ZFAB modified cementitious specimens with different Ag dosages are prepared and the characteristics and photocatalytic performance of the prepared samples are investigated.It is observed that the multi-level pore structure of ZFAB can improve the exposure degree of TiO2 in a cement system and is also useful to enhance the photocatalytic efficiency.With an increment of the amounts of Ag particles in the TiO2/ZFAB modified cementitious samples,the photocatalytic activities increased first and then decreased.The optimal Ag@TiO2/ZFAB modified cementitious sample reveals the maximum reaction rate constant for degrading benzene（9.91×10^-3 min^-1）,which is approximately 3 and 10 times higher than those of TiO2/ZFAB and TiO2 modified samples,respectively.This suggests that suitable Ag particles coupled with a ZFAB carrier could effectively enhance the photocatalytic effects and use of TiO2 in a cement system.Thus,ZFAB as a carrier could provide a potential method for a high efficiency engineering application of TiO2 in the construction field.

Importance of metal location in M-H zeolite for synergistically catalyzing dimethyl ether carbonylation

Mordenite(MOR)has shown great potential to catalyze dimethyl ether(DME)carbonylation to methyl acetate(MA)in industry.The synergy between metal species and Brønsted acid sites accelerates DME conversion.Here we designed and prepared two catalysts with different Ag locations by seed-directed growth method and two-step impregnation method(named as Ag@HMOR and Ag/HMOR-out,respectively),to explain the effect of Ag location on catalytic performance.The results of TEM,XPS,CO-IR and UV–Vis showed that Ag species mainly presented as Ag^(0) species over both Ag@HMOR and Ag/HMOR-out.Meanwhile,Ag^(0) species mainly located in the micropores of Ag@HMOR,while as for Ag/HMOR-out,Ag^(0) mainly existed on external surface.After comparing the performance of the catalysts with different Ag positions,we confirmed that the Ag^(0) species encapsulated in the channels of HMOR promoted the DME carbonylation,which revealed the importance of spatial adjacency on the acid-metal catalysts.

Electrosynthesis and catalytic properties of silver nano/microparticles with different morphologies

Electrosynthesis of powdery silver particles can be effectively carried out with an H20-oleic acid or an H20-glycerol mix solvent （volume ratio 1：1） as the electrolytic medium and AgN03 as the supporting electrolyte. Experimental results indicate that the presence or absence of the surfactant sodium dodecyl sulfate （SDS） and the choice of electrolytic medium have a significant impact on the shape and size of the prepared Ag particles. With H20-glycerol as the electrolytic medium, spherical Ag nanoparticles can be obtained in the presence of SDS （0.6g/L）, while an Ag sample electrodeposited without SDS has a dendritic microcrystalline structure. For the reduction of methyl orange （MO） and methylene blue （MB） with NaBH4 as the reducing agent, the spherical Ag nanoparticles exhibit much better catalytic activity than the dendritic Ag microparticles. Further investigations show that surface modification by an oleic acid medium could greatly improve the catalytic activity of the electrodeposited Ag particles for the reduction of MO and MB.