Abstract. Kinetic study on the removal of zinc(II), copper(II), lead(II) and cadmium(II) from the aqueous solutions using multi-walled carbon nanotubes (MWNTs) was carried out to examine the temperature effect on the adsorption of zinc(II), copper(II), lead(II) and cadmium(II) as well as to explore the potentiality of using carbon nanotubes as a promising adsorbent for environmental remediation. Multi-walled carbon nanotubes were characterized by BET (Brunauer-Emmett-Teller), FE-SEM (Field emission scanning electron microscopy), and DPASV (differential pulse anodic stripping voltammetry). Adsorption experiments were carried out and comparisons with the previous work were made. Experimental results showed that the multi-walled carbon nanotubes can successfully remove zinc(II), copper(II), lead(II) and cadmium(II) from aqueous solutions. Increasing solution temperature can significantly improve the removal efficiency because of the endothermic nature of adsorption process. The kinetics of zinc(II), copper(II), lead(II) and cadmium(II) adsorption on multi-walled carbon nanotubes were analyzed, and the calculation results showed that the heavy metal ions adsorption is a pseudo-second-order process, and its capacity increases with increasing solution temperature. The binding of the metal ions by the multi-walled carbon nanotubes was evaluated from the adsorption capacities and found in the following order: copper(II) > lead(II) > zinc(II) > cadmium(II). Finally, multi-walled carbon nanotubes demonstrated that they are a promising adsorbent for the removal of heavy metal ions from aqueous solutions.

The hetero-/homogeneous combustion and interaction of hydrogen-fueled catalytic microreactors were investigated numerically. A two-dimensional CFD (computational fluid dynamics) model was developed, using elementary homogeneous and heterogeneous chemical reaction schemes, surface radiation heat transfer, heat conduction in the solid wall, and external heat losses. Computations were carried out to study the effects of the wall thermal conductivity, equivalence ratio, microreactor dimension, and inlet velocity on combustion characteristics, flame stability, and hetero-/homogeneous interaction. Despite the micro-scale, large transverse gradients in species mass fractions and temperature exist in the fluid and large axial gradients in temperature may exist in the walls. Wall thermal conductivity is crucial in determining the flame stability, as the walls transfer heat upstream for ignition of the cold incoming reactants but at the same time are responsible for heat losses. Combustible mixtures with compositions away from the stoichiometric point decrease the homogeneous chemistry contribution and the operating temperature. The microreactor dimension and inlet velocity have a strong effect on homogeneous flame stability. Smaller microreactors result in extinction because of the inhibition of homogeneous combustion induced by heterogeneous reaction; larger microreactors result in blowout due to the reduction of the heterogeneous contribution. Hetero-/homogeneous interaction maps were constructed in terms of microreactor dimension and inlet velocity.

Kinetic study on the removal of zinc(II), copper(II), lead(II) and cadmium(II) from the aqueous solutions using multi-walled carbon nanotubes (MWNTs) was carried out to examine the temperature effect on the adsorption of zinc(II), copper(II), lead(II) and cadmium(II) as well as to explore the potentiality of using carbon nanotubes as a promising adsorbent for environmental remediation. Multi-walled carbon nanotubes were characterized by BET (Brunauer-Emmett-Teller), FE-SEM (Field emission scanning electron microscopy), and DPASV (differential pulse anodic stripping voltammetry). Adsorption experiments were carried out and comparisons with the previous work were made. Experimental results showed that the multi-walled carbon nanotubes can successfully remove zinc(II), copper(II), lead(II) and cadmium(II) from aqueous solutions. Increasing solution temperature can significantly improve the removal efficiency because of the endothermic nature of adsorption process. The kinetics of zinc(II), copper(II), lead(II) and cadmium(II) adsorption on multi-walled carbon nanotubes were analyzed, and the calculation results showed that the heavy metal ions adsorption is a pseudo-second-order process, and its capacity increases with increasing solution temperature. The binding of the metal ions by the multi-walled carbon nanotubes was evaluated from the adsorption capacities and found in the following order: copper(II) > lead(II) > zinc(II) > cadmium(II). Finally, multi-walled carbon nanotubes demonstrated that they are a promising adsorbent for the removal of heavy metal ions from aqueous solutions.

The hetero-/homogeneous combustion and interaction of hydrogen-fueled catalytic microreactors were investigated numerically. A two-dimensional CFD (computational fluid dynamics) model was developed, using elementary homogeneous and heterogeneous chemical reaction schemes, surface radiation heat transfer, heat conduction in the solid wall, and external heat losses. Computations were carried out to study the effects of the wall thermal conductivity, equivalence ratio, microreactor dimension, and inlet velocity on combustion characteristics, flame stability, and hetero-/homogeneous interaction. Despite the micro-scale, large transverse gradients in species mass fractions and temperature exist in the fluid and large axial gradients in temperature may exist in the walls. Wall thermal conductivity is crucial in determining the flame stability, as the walls transfer heat upstream for ignition of the cold incoming reactants but at the same time are responsible for heat losses. Combustible mixtures with compositions away from the stoichiometric point decrease the homogeneous chemistry contribution and the operating temperature. The microreactor dimension and inlet velocity have a strong effect on homogeneous flame stability. Smaller microreactors result in extinction because of the inhibition of homogeneous combustion induced by heterogeneous reaction; larger microreactors result in blowout due to the reduction of the heterogeneous contribution. Hetero-/homogeneous interaction maps were constructed in terms of microreactor dimension and inlet velocity.