posted on 2023-12-27, 14:05authored byPooja Sahu, Sk. Musharaf Ali
Inspired
by the enhanced water permeability of carbon nanotubes
(CNTs), molecular dynamics simulations were performed to investigate
the transport behavior through nanotubes made of boron nitride (BNNT),
silicon carbide (SiC), and silicon nitride (SiN) alongside carbon
nanotubes (which have different hydrophobic attributes) considering
their implication for reverse osmosis (RO) membranes under different
practical environments. According to our findings, not only do CNTs
but also other kinds of nanotubes exhibit transition anomalies with
increasing diameter. Utilizing the robust two-phase thermodynamic
(2PT) methods, the current examinations shed light on thermodynamic
origin of favorable water filling of these nanotubes. The results
show that regardless of the nanotube material, the filling of water
inside small nanopores (d < 10 Å) as well
as within pores of diameter larger than 15 Å will always be favored
by the entropy of filling. However, the entropic preference for filling
nanotubes with a diameter of 10–15 Å depends on the constituent
material. In particular, the enhancement in total entropy of confined
water was mainly due to the increased rotational freedom of confined
water molecules. The thermodynamic origin of water transport was correlated
with the structural and fluidic behavior of water inside these nanotubes.
The observed data for density, flow, structure correlation functions,
water–water coordination, tetrahedral order parameter, hydrogen
bonds, and density of states functions quantitatively support the
observed entropy behavior. Of critical importance is that the present
study demonstrates the effectiveness of RO filtration using nanotubes
of boron nitride rather than carbon. Furthermore, it was found that
one should avoid the use of silicon nanotubes unless filtration needs
to be performed under harsh environments where nanotube of other materials
cannot survive. Specifically, the results show that both the structural
and dynamic properties of water confined in BNNTs are similar to those
of CNT’s, and for SiNT it is similar as SiC. Our results show
that besides the nanotube material, the chirality index of the nanotube
also plays a significant role in determining the structure, dynamics
and thermodynamics of confined water molecules