CO methanation reaction over the Ni/Al2O3 catalysts for synthetic natural gas production was systematically investigated by tuning a number of parameters, including using different commercial Al2O3 supports and varying NiO and MgO loading, calcination temperature, space velocity, H2/CO ratio, reaction pressure, and time, respectively. The catalytic performance was greatly influenced by the above-mentioned parameters. Briefly, a large surface area of the Al2O3 support, a moderate interaction between Ni and the support Al2O3, a proper Ni content (20 wt %), and a relatively low calcination temperature (400 °C) promoted the formation of small NiO particles and reducible β-type NiO species, which led to high catalytic activities and strong resistance to the carbon deposition, while addition of a small amount of MgO (2 wt %) could improve the catalyst stability by reducing the carbon deposition; other optimized conditions that enhanced the catalytic performance included high reaction pressure (3.0 MPa), high H2/CO ratio (≥3:1), low space velocity, and addition of quartz sand as the diluting agent in catalyst bed. The best catalyst combination was 20–40 wt % of NiO supported on a commercial Al2O3 (S4) with addition of 2–4 wt % of MgO, calcined at 400–500 °C and run at a reaction pressure of 3.0 MPa. On this catalyst, 100% of CO conversion could be achieved within a wide range of reaction temperature (300–550 °C), and the CH4 selectivity increased with increasing temperature and reached 96.5% at a relatively low temperature of 350 °C. These results will be very helpful to develop highly efficient Ni-based catalysts for the methanation reaction, to optimize the reaction process, and to better understand the above reaction.

The currently applied disinfection methods during water treatment provide effective solutions to kill pathogens, but also generate harmful byproducts, which are required to be treated with additional efforts. In this work, an alternative and safer water disinfection system consisting of silver nanoparticle/multiwalled carbon nanotubes (Ag/MWNTs) coated on a polyacrylonitrile (PAN) hollow fiber membrane, Ag/MWNTs/PAN, has been developed. Silver nanoparticles of controlled sizes were coated on polyethylene glycol-grafted MWNTs. Ag/MWNTs were then covalently coated on the external surface of a chemically modified PAN hollow fiber membrane to act as a disinfection barrier. A continuous filtration test using E. coli containing feedwater was conducted for the pristine PAN and Ag/MWNTs/PAN composite membranes. The Ag/MWNT coating significantly enhanced the antimicrobial activities and antifouling properties of the membrane against E. coli. Under the continuous filtration mode using E. coli feedwater, the relative flux drop over Ag/MWNTs/PAN was 6%, which was significantly lower than that over the pristine PAN (55%) at 20 h of filtration. The presence of the Ag/MWNT disinfection layer effectively inhibited the growth of bacteria in the filtration module and prevented the formation of biofilm on the surface of the membrane. Such distinctive antimicrobial properties of the composite membrane is attributed to the proper dispersion of silver nanoparticles on the external surface of the membrane, leading to direct contact with bacterium cells.

We report a remarkably simple and efficient method for the preparation of colloidal nanohybrids consisting of Fe 3 O 4 nanoparticles and nitrate-containing MgAl-layered double hydroxide (LDH) nanocrystals. The electrostatic interaction between the negatively charged magnetite nanoparticles and the positively charged LDH nanocrystals is sufficient to induce the formation of stable self-assembly of the two components. At a mass ratio of 1 : 0.3 (LDH:Fe 3 O 4 ), all Fe 3 O 4 nanoparticles are attached on the LDH nanocrystals. The resulting nanohybrids maintained an overall positive zeta potential of +42 mV and can form a stable colloidal suspension in water. Separation/re-dispersion of the nanohybrids in the aqueous phase can be easily achieved in the presence/absence of an external magnetic field. The combination of these unique properties allows the nanohybrids to exhibit superior performance in the treatment of organic dyes in wastewater. The colloidal suspension of the nanohybrids leads to fast adsorption kinetics and high adsorption capacity of the acid organic dyes via quick surface adsorption. In addition, the spent nanohybrids can be easily recycled after catalytic regeneration by advanced oxidation technology.

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Uniform NiO, α-Fe2O3, ZnO, CuO and Ga2O3 hollow nanospheres consisting of a shell of closely packed nanoparticles with a shell wall thickness of a few tens of nanometers have been successfully synthesized on a large scale by controlled precipitation of metal cations with urea in the presence of carbonaceous saccharide nanospheres as hard templates. In addition, it is interesting to find that the single-phase transition metal oxides of NiO and α-Fe2O3 can form ball-in-ball hollow nanoarchitectures by this simple approach. Furthermore, it is demonstrated that direct size control of the oxide hollow nanospheres can be achieved by using carbon templates of different diameters. This method could be extended to the synthesis of many other metal oxide hollow nanospheres. The hollow nanostructured metal oxides might be found to have potential applications in many fields such as catalyst supports, catalysis, drug delivery, chemical/biological separation, sensing, etc.

Simple and facile processes to produce silver nanoparticles deposited layered double hydroxide (Ag-LDH) coatings are reported. High quality nanoporous LDH coatings are obtained under hydrothermal conditions via an improved in situ growth method by immersing the substrates in LDH suspensions after removal of free electrolytes. Different types of substrates including metal, ceramics, and glass with planar and non-planar surfaces can all be coated with the oriented LDH films with strong adhesion. The pore size can be easily tuned by changing the metal:NaOH ratio during the precipiation process of LDH precursors. In the presence of LDH coatings, silver ions can be readily reduced to metallic silver nanoparticles (Ag NPs) in aqueous solutions. The resulting Ag NPs are incorporated evenly on LDH surface. The Ag-LDH coating exhibits excellent and durable antimicrobial activities against both Gram-negative (E. Coli and P. Aeruginosa) and Gram-positive (B. Subtilis and S. Aureus) bacteria. Even at the 4th recycled use, more than 99% of all types of bacteria can be killed. Moreover, the Ag-LDH coating can also effectively inhibit the bacterial growth and prevent the biofilm formation in the nutrient solutions. These newly designed Ag-LDH coatings may offer a promising antimicrobial solution for clinical and environmental applications.

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We report the direct assembly of anisotropic layered double hydroxide nanocrystals from a stable colloidal suspension onto spherical templates in a single step for the generation of hollow nanospheres. This approach does not involve the conventional exfoliation/LBL-stacking process. LDH hollow nanospheres intercalated with drug anions are fabricated on the basis of the memory effect.