Shijian Zhou

In situ incorporation of well-dispersed Cu–Fe oxides in the mesochannels of AMS and their utilization as catalysts towards the Fenton-like degradation of methylene blue

Multi-components active metal oxide-supported catalysts are highly promising in heterogeneous catalysis due to some special promoting effects. In this study, by the controllable amount of Cu, Cu–Fe decorated anionic surfactant-templated mesoporous silica (CuxFe/AMS) was directly prepared. The obtained catalysts were characterized by X-ray diffraction, N2 adsorption–desorption, inductively coupling plasma emission spectroscopy, scanning electron microscopy, transmission electron microscopy, UV–visible, hydrogen temperature-programmed reduction, and X-ray photoelectron spectroscopy techniques. The results revealed that bimetallic Cu–Fe oxides were directly formed and highly dispersed in the mesochannels during the calcinations and the introduction of Cu2+ and Fe2+ on the micelles has influence on the structure properties. As compared to the monometallic Fe-modified AMS, the presence of Cu promotes the effects between Fe species and silica wall, leading to the better dispersion of Fe in the mesochannels of AMS. Finally, a series of Cu–Fe-modified AMS were used as Fenton-like catalysts and exhibited good catalytic activity in the degradation of methylene blue (MB), which resulted from high dispersion of Fe species and synergetic effect between Cu and Fe active sites. 1.0 was the optimum molar ratio of Cu2+ to Fe2+ ions to achieve the best catalytic activity and stability.

An iron-based micropore-enriched silica catalyst: in situ confining of Fe2O3 in the mesopores and its improved catalytic properties

Surface exposed catalytic active species are thought to be responsible for overall catalytic activity and selectivity. In this paper, controllable contents of iron oxides were in situ introduced into the inner surface of anionic surfactant-templated mesoporous silica (AMS) by the metal-modified anionic surfactant templating route, in which anionic micelles decorated with different amounts of Fe2+ were direct utilized to assemble with organosilicate. The characterization results demonstrated that, after thermal treatments, Fe2O3 species were in situ formed and highly-dispersed in the channels of AMS, and the pore size was accordingly tailored to the microporous level (<2 nm). In each AMS catalyst, Fe2O3 showed better dispersion and stability compared with the post-impregnated method. Moreover, the catalytic performances of phenol hydroxylation on the as-synthesized catalysts were significantly enhanced, and the optimal catalyst (Fe/Si = 3.5 wt%) gave a phenol conversion of 44.3% with a selectivity of 82.6% to dihydroxybenzene. By comparison with some reference mesoporous silica catalysts (0.15Fe/MCM-41 and 0.15Fe/SBA-15), the iron-based micropore-enriched silica catalyst (Fe/AMS) gave an obviously higher selectivity to dihydroxybenzene. Finally, the optimal catalyst was examined for at least 5 runs in phenol hydroxylation.

Template-induced in situ dispersion of enhanced basic-sites on sponge-like mesoporous silica and its improved catalytic property

Catalytic performance of heterogeneous catalysis is strongly dependent on the dispersity of catalytic active sites, and especially a high exposure of the unit active phase is promising for the overall catalytic process. In this study, a novel strategy was developed to fabricate an unprecedented CaO-based mesoporous solid strong base catalyst. Relying on the physicochemical assembly of Ca2+ in the interface between a micelle and siliceous wall, thin-layer-like calcium oxide species were formed in situ and dispersed in the mesochannels of silica. Wherein, the gradual coverage of CaO on the mesoporous wall was controlled by adjusting the amounts of Ca2+ on alkylamine micelles. Interestingly, a novel sponge-like microscale structure of silica was discovered in the CaO-based mesoporous-composites for the first time, which completely differs from the reported mesoporous silica. More importantly, the introducing of a CaO solid base on the pore wall is nearly non-destructive for the textural properties of the mesoporous matrix. The direct template-induced mesoporous solid strong base not only received extremely dispersed and unexpected enhanced strong basic sites (CO2-desorption temperature ≥718 °C), but also avoided repeated thermal processes for the degradation of the basic resource, and saved energy and time. This heterogeneous alkaline catalyst shows excellent catalytic activity for the synthesis of dimethyl carbonate under a milder reaction condition (30 °C, 25 min) and holds stability and reusability beyond comparison with the conventional catalysts. The dispersed and enhanced strong basic sites, combined with excellent mesoporous properties, are demonstrated to be responsible for such a high catalytic performance.

Aminosilane decorated carbon template-induced in situ encapsulation of multiple-Ag-cores inside mesoporous hollow silica

A dispersed and stable catalytic active phase and a protective reaction environment are acknowledged as ideal metal catalyst characteristics. In this paper, a cores@shell structure of microreactor with a well-dispersed active phase of multiple free-Ag-cores, hollow cavity and protective mesoporous shell was prepared by a simple and novel construction approach. The organic ligand of aminosilane (APTES) was directly incorporated on carbon nanospheres to anchor Ag ions as a metallotemplate, which avoids the tedious steps of conventional methods, and then the sacrificed metallotemplate was employed for directly fabricating the special hollow mesoporous silica microreactors. As a result, multiple free active Ag-cores were in situ produced and encapsulated in the cavity of hollow mesoporous silica during the thermal process. The important evidence of the configuration including a big hollow cavity containing active multiple-Ag nanoparticles and a mesoporous SiO2-shell can be demonstrated with efficient techniques including XRD, FT-IR, XPS, BET, SEM and TEM. Just as expected, the catalyst as a functional microreactor exhibited a high catalytic activity for the liquid-reduction of 4-nitrophenol, and the increasing dosage of used catalyst contributes to the enhancing of catalytic activity. The methodology demonstrated here provides a new insight for the fabrication of versatile functional nanomaterials with noble or transition metals inside a hollow shell.

Thermal-induced surface defective Co/Fe–Co planar hybrid composite nanosheet with enhanced catalytic activity in the Fenton-like reaction

Surface defective or heterojunction sites of catalysts generally afford remarkable catalytic activity thanks to their high-surface-energy. Regularly-generating multiple defective sites on the surface of a catalyst is exceedingly promising in many reactions. In this study, we report an unexpected Co/Fe–Co planar hybrid composite nanosheet with serried surface defects including surface biphasic junction sites or defective holes. A facile thermal-induced process was applied to trigger the generation of defective sites on planar Co/Fe–Co hydroxides. Through a controlled thermal process, massive serried CoO nanocrystals were in situ dissolved out of the surface of cobalt hydroxide, while defective surface holes were formed on the Fe-doped Co(OH)2 nanosheets under a prolonged thermal procedure. The morphology and microscale structure of the resulting Co/Fe–Co hybrid 2-dimensional (2D) composites were systematically examined by virtue of various characterization techniques. As expected, the obtained surface defective Co/Fe–Co planar composites showed obviously enhanced catalytic activity in the Fenton-like reaction. Based on a catalytic study, we proved that the CoO nanocrystals densely-distributed on thinlayer Co(OH)2. Uniformly-introduced Fe heteroatoms in the inter-structure of Co(OH)2, along with the formed surface defective holes on Fe–Co hybrid composites, are synergistically responsible for increased catalytic removal efficiency of MB in the presence of peroxomonosulfate.