Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields

Graphene-based materials can have well-defined nanometer pores and can exhibit low frictional water flow inside them, making their properties of interest for filtration and separation. We investigate permeation through micrometer-thick laminates prepared by means of vacuum filtration of graphene oxide suspensions. The laminates are vacuum-tight in the dry state but, if immersed in water, act as molecular sieves, blocking all solutes with hydrated radii larger than 4.5 angstroms. Smaller ions permeate through the membranes at rates thousands of times faster than what is expected for simple diffusion. We believe that this behavior is caused by a network of nanocapillaries that open up in the hydrated state and accept only species that fit in. The anomalously fast permeation is attributed to a capillary-like high pressure acting on ions inside graphene capillaries.

/pdf/precise-and-ultrafast-molecular-sieving-through-graphene-20s9r4k8z6.pdf

Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes

Membranes have an increasingly important role in alleviating water scarcity and the pollution of aquatic environments. Promising molecular-level design approaches are reviewed for membrane materials, focusing on how these materials address the urgent requirements of water treatment applications.

Materials for next-generation desalination and water purification membranes

https://purehost.bath.ac.uk/ws/files/9234686/JMS_2011.pdf

A review of reverse osmosis membrane materials for desalination—Development to date and future potential

We report a novel procedure to synthesize a new type of water separation membrane using graphene oxide (GO) nanosheets such that water can flow through the nanochannels between GO layers while unwanted solutes are rejected by size exclusion and charge effects. The GO membrane was made via layer-by-layer deposition of GO nanosheets, which were cross-linked by 1,3,5-benzenetricarbonyl trichloride, on a polydopamine-coated polysulfone support. The cross-linking not only provided the stacked GO nanosheets with the necessary stability to overcome their inherent dispensability in water environment but also fine-tuned the charges, functionality, and spacing of the GO nanosheets. We then tested the membranes synthesized with different numbers of GO layers to demonstrate their interesting water separation performance. It was found that the GO membrane flux ranged between 80 and 276 LMH/MPa, roughly 4–10 times higher than that of most commercial nanofiltration membranes. Although the GO membrane in the present deve...

Enabling graphene oxide nanosheets as water separation membranes.

Ionic and molecular sieving membranes that enable fast solute separations from aqueous solutions are essential for processes such as water purification and desalination, sensing, and energy production ( 1 – 3 ). The two-dimensional structure and tunable physicochemical properties of graphene oxide (GO) offer an exciting opportunity to make a fundamentally new class of sieving membranes by stacking GO nanosheets ( 4 – 6 ). In the layered GO membrane, water molecules permeate through the interconnected nanochannels formed between GO nanosheets and follow a tortuous path primarily over the hydrophobic nonoxidized surface rather than the hydrophilic oxidized region of GO ( 7 ). The nearly frictionless surface of the non-oxidized GO facilitates the extremely fast flow of water molecules ( 5 ). On page 752 of this issue, Joshi et al. ( 8 ) further report that ions smaller in size than the GO nanochannel can permeate in the GO membrane at a speed orders of magnitude faster than would occur through simple diffusion. Size exclusion appears to be the dominant sieving mechanism.

http://science.sciencemag.org/content/sci/343/6172/740.full.pdf

Graphene Oxide Membranes for Ionic and Molecular Sieving

Organic fouling of forward osmosis membranes: Fouling reversibility and cleaning without chemical reagents

Chemical and physical aspects of organic fouling of forward osmosis membranes

In an era of graphene-based nanomaterials as the most widely studied two-dimensional (2D) materials for enhanced performance of devices and systems in numerous environmental applications, molybdenum disulfide (MoS2) nanosheets stand out as a promising alternative 2D material with many excellent physicochemical, biological, and mechanical properties that differ significantly from those of graphene-based nanomaterials, potentially leading to new environmental phenomena and novel applications. This Critical Review presents the latest advances in the use of MoS2 nanosheets for important water-related environmental applications such as contaminant adsorption, photocatalysis, membrane-based separation, sensing, and disinfection. Various methods for MoS2 nanosheet synthesis are examined, and their suitability for different environmental applications is discussed. The unique structure and properties of MoS2 nanosheets enabling exceptional environmental capabilities are compared with those of graphene-based nanoma...

Baoxia Mi

Papers

Enabling graphene oxide nanosheets as water separation membranes.

Graphene Oxide Membranes for Ionic and Molecular Sieving

Organic fouling of forward osmosis membranes: Fouling reversibility and cleaning without chemical reagents

Chemical and physical aspects of organic fouling of forward osmosis membranes

Environmental Applications of 2D Molybdenum Disulfide (MoS2) Nanosheets