Selective molecular separation of lignin model compounds by reduced graphene oxide membranes from solvent-water mixture

High flux and complete dyes removal from water by reduced graphene oxide laminate on Poly Vinylidene Fluoride/graphene oxide membranes

Dyes molecules are the most common pollutants of wastewater in the environment from the textile industry to numbers of technologies include dyeing, printing, and painting procedures. Among membrane-based separation approaches as established methods in the water treatment industry, polymers attracted massive attention in the production of membranes due to their low cost and high-performance filtration of pollutants. However, hydrophobicity and low speed of filtration along with limited decontamination performance against some of the dyes, demand new approaches and membranes to overcome drawbacks points. Herein, a new design introduced including a support layer made by Poly Vinylidene Fluoride (PVDF)/Graphene Oxide (PGO) composite membrane via immersion precipitation process and a thin layer (≤100 nm) of reduced graphene oxide (rGO) deposited (as an active layer) through a simple vacuum filtration method. It has been observed that the presence of the GO sheets in the PGO composite improved the hydrophilicity of the membrane, water flux (from ~90 L m^-2 h^-1 bar^-1 in pristine PVDF to ~1690 L m^-2 h^-1 bar^-1 in PGO), and anti-fouling property. By deposition of rGO laminate on PGO support, dyes separation as high as ~99% can be achieved for most of the cationic and anionic dyes due to electrostatic adsorption, π-π interactions and molecular sieving. This approach opens new insight on hybrid designs for graphene-polymers based membrane toward efficient and fast removal of pollutants from wastewater.

Reduced graphene oxide-metal nanoparticle composite membranes for environmental separation and chloro-organic remediation

This study explores the integration of separation performance of rGO membrane with heterogeneous oxidation reactions for remediation of organic contaminants from water. Herein, an approach was introduced based on layer-by-layer assembly for functionalizing rGO membranes with polyacrylic acid and then by in situ synthesis of Fe based reactive nanoparticles. TEM characterization of the cross-section lamella of the membranes showed a high density of nanoparticles (12% Fe) in the functionalized domain, signifying the importance of polyacrylic acid for in situ synthesis of nanoparticles. The membranes exhibited a pure water permeability of 1.9 LMH bar⁻¹. The membranes had low to moderate salt retention, and more than 90% neutral red retention (organic probe molecule, size: 1.2 nm). The membranes also exhibited high retention of humic acids (80%), preventing these organics from entering the reactive domain, and thus potentially reducing the formation of undesired by-products. A persulfate mediated oxidative pathway was employed to demonstrate the reactive removal of organic contaminants. The membranes achieved >95% conversion by convectively passing 2 mM persulfate feed at a transmembrane pressure of 0.4 bar. Successful degradation of TCE (up to 61%) was achieved in a single pass by convective flowing of the feed solution through the membrane, generating up to 80% of the theoretical maximum chloride as one of the byproducts. Elevated temperatures significantly enhanced persulfate mediated TCE oxidation extent from 24% at 23 °C to 54% at 40 °C under batch operating conditions.

This study explores the integration of separation performance was achieved in a loose nanofiltration regime with heterogeneous oxidation reactions for remediation of organic contaminants from water.