Fe3O4 decorated multi-walled carbon nanotube (Fe3O4/MWCNT) nanocomposites were synthesized by co-precipitation process and used as heterogeneous Fenton catalyst for degradation of phenol and p-nitrophenol (p-NP). The Fe3O4 nanoparticles with size less than 20 nm were well-dispersedly coated on the surface of MWCNTs at relatively low loading. Some aggregations appear at high Fe3O4 content in composite. The Fe3O4/MWCNT with about 25 wt.% of Fe3O4 is the most cost-effective catalyst compared with others, whose phenol conversion and COD removal rates could, respectively, reach to 99.20 and 58.09%. And a high H2O2 utilization efficiency was achieved (about 132.41%) for this catalyst. For the p-NP degradation, the optimal reaction condition was that: 2.0 mg/L of catalyst dosage, 3 mmol/L of initial H2O2 concentration, 3 of pH value, and 40 °C of reaction temperature. At this condition, the removal rates of p-NP and COD in 120 min achieved 97.16 and 67.71%, respectively. And the Fe3O4/MWCNT nanocomposite also exhibits an acceptable stability and reusability.

Magnetite@carbon (Fe3O4@C) composites were prepared using three kinds of Fe3O4 nanoparticles (NPs). All the Fe3O4@C composites could be easily separated from water by an external magnet. The Fe3O4 NPs synthesized by a microreactor system have the smallest size and narrowest size distribution among the three kinds of Fe3O4 NPs. The saturated capacity of the Fe3O4@C composite originating from microreactor-prepared Fe3O4 NPs to absorb Rhodamine B at 20∘C exceeds 135 mg g−1, which is 1.35 times as much as the value of the Fe3O4@C composite originating from traditional Fe3O4 NPs. This value for the Fe3O4@C composite using commercial Fe3O4 NPs as core is only 76 mg g−1. The Fe3O4@C composite using microreactor-prepared Fe3O4 NPs also has good retrievability and reusability.

•Surface modification of MWCNTs is crucial for property improvement of RTV silicone rubber composites.•Well dispersion of MWCNTs treated by polydimethylsiloxane solution in silicone rubber was achieved.•Properties of silicone rubber were improved by using polydimethylsiloxane solution modified MWCNTs.Room temperature vulcanized (RTV) silicone rubber composites reinforced by multi-walled carbon nanotubes (MWCNTs) were prepared. The effect of surface modification methods and MWCNT contents on the properties of the RTV silicone rubber composites was investigated. The properties of the composites were improved when the treated MWCNTs were used. After treated by polyester-modified polydimethylsiloxane solution (BKY-310), the MWCNTs were uniformly dispersed in the silicone rubber matrix. When 5 phr of MWCNTs was added, the composite achieved good comprehensive performance. Its tensile strength, tear strength, elongation and onset decomposition temperature reach 2.0 MPa, 11.7 kN/m, 238% and 510 °C, respectively. But the above said values for the composite with untreated MWCNTs are only 1.1 MPa, 7.0 kN/m, 83% and 484 °C, respectively.

Multi-walled carbon nanotubes (MWCNTs) with large inner diameter were synthesized by the catalytic chemical vapor deposition method using HBO3 as the accessorial catalyst in reaction precursors. A ratio Din/Dout is defined as an index to evaluate the hollow degree of MWCNTs, where Din and Dout are the inner and outer diameter of one CNT, respectively. When no HBO3 was added in the reaction mixtures, the MWCNTs are straight with thick wall. The average Din/Dout value is only 0.08 ± 0.02. The X-ray diffraction (XRD) result shows the relatively low crystallinity. When HBO3 was added in the reaction precursors, the MWCNTs have large inner cavity and the average Din/Dout value reaches 0.57 ± 0.10. The crystallinity was also improved remarkably. These results indicate that HBO3 in the catalyst system has great influence on the growth of MWCNTs.Highlights► The inner diameter of multi-walled carbon nanotubes (MWCNTs) was enlarged remarkably by adding HBO3 in the reaction precursors. ► The crystallinity of MWCNTs was improved by adding HBO3 in the reaction precursors. ► This method contributes to the understanding of nanotube growth mechanism.