Studies on the solubilization of aqueous methylene blue in surfactant using MEUF

Ganzoury M, Zhang N, de Lannoy CF. Nanocomposite Polymeric Membranes for Organic Micropollutant Removal: A Critical Review

The prevalence of organic micropollutants (OMPs) and their persistence in water supplies have raised serious concerns for drinking water safety and public health. Conventional water treatment technologies, including adsorption and biological treatment, are known to be insufficient in treating OMPs and have demonstrated poor selectivity toward a wide range of OMPs. Pressure-driven membrane filtration has the potential to remove many OMPs detected in water with high selectivity as a membrane's molecular weight cutoff (MWCO), surface charge, and hydrophilicity can be easily tailored to a targeted OMP's size, charge and octanol-water partition coefficient (Kow). Over the past 10 years, polymeric (nano)composite microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes have been extensively synthesized and studied for their ability to remove OMPs. This review discusses the fate and transport of emerging OMPs in water, an assessment of conventional membrane-based technologies (NF, reverse osmosis (RO), forward osmosis (FO), membrane distillation (MD) and UF membrane-based hybrid processes) for their removal, and a comparison to the state-of-the-art nanoenabled membranes with enhanced selectivity toward specific OMPs in water. Nanoenabled membranes for OMP treatment are further discussed with respect to their permeabilities, enhanced properties, limitations, and future improvements.

Physicochemical Studies on the Interaction between Sodium Dodecyl Sulfate and Methylene Blue in Methanol-Water Mixed Solvent Media

The surface activity and the process of micellization of sodium dodecyl sulfate (SDS) with methylene blue (MB) in a methanol-water mixed solvent system were investigated by tensiometry and conductometry at 298.15 K. The measurements of surface tension and conductivity of SDS-MB complex were carried up to 0.3 volume fractions of methanol because the resulting complex appeared turbid above 0.3 volume fractions of methanol. The critical micelle concentration (CMC) of the SDS was determined from both tensiometry and conductometry. The CMC of SDS increased with the increasing volume fraction of methanol due to the inclusion of methanol in the micelles and decreased in the presence of methylene blue due to the reduction of electrostatic repulsion within the anionic moiety of SDS by the positive charge of the added dye. Different properties like surface excess concentration $\left({\mathrm{\Gamma }}_{\max }\right)$ , minimum surface area $\left(A_{\text{min}}\right)$ , Gibbs free energy of micellization $\left(\mathrm{\Delta }{G}_{\mathrm{m}}^o\right)$ , surface pressure ( ${\pi }_{\text{CMC}}$ ), efficiency of a surfactant ( $\text{p}{C}_{20}$ ), packing parameter $\left(P\right)$ , and standard free energy interfacial adsorption $\left(\mathrm{\Delta }{G}_{\text{ads}}^o\right)$ of SDS in the absence/presence of MB were calculated. On the basis of $\mathrm{\Delta }{G}_{\mathrm{m}}^o$ values, it was noticed that the increasing volume fraction of methanol disfavors the micellization of SDS, while the presence of MB increased the efficiency of SDS making the micellization process more spontaneous.

Micellar-enhanced ultrafiltration for the solubilization of various phenolic compounds with different surfactants

Micellar-enhanced ultrafiltration (MEUF) was applied to the separation of phenolic compounds p-nitrophenol (PNP), p-chlorophenol (PCP), p-cresol (PC) and phenol (P) from effluents using a hydrophilic polyethersulfone ultrafiltration membrane. Cationic cetylpyridinium chloride (CPC), nonionic TX-100 and anionic sodium dodecyl benzene sulfonate (SDBS) were chosen as the surfactants. Several important parameters, i.e. the separation efficiency, the distribution coefficient of phenolic compounds and the removal ratio of surfactants, were investigated. It was shown that the separation efficiency and the distribution coefficient of phenolic compounds ascended with the increasing surfactant concentration and could be arranged as the following order: PNP>PCP>PC>P. Moreover, in the case of phenolic compound separation, CPC achieved the highest treatment efficiency, and the separation efficiency of SDBS was a little lower than that of TX-100. The removal ratios of the same surfactant when treating different phenolic effluents were nearly similar. However, when treating the same phenolic compound, the sequence of the surfactant rejection was in the following order: TX-100>CPC>SDBS. These results indicate that CPC has a distinct superiority in the treatment of phenolic effluents via the MEUF process, and PNP easily solubilizes in the surface of the micelles.

Influence of micelle properties on micellar-enhanced ultrafiltration for chromium recovery

An investigation of micelle properties on the recovery of chromium for micellar enhanced ultrafiltration (MEUF) process was conducted using cationic surfactant of cetyltrimethylammonium bromide (CTAB). The relationship between degree of ionization, micellar sizes and chromium removal were determined in this study. The results showed that the complete ionization for CTA+ and Br- was observed for CTAB lower than 0.72 mM and aggregation initiated at concentration of CTAB higher than 0.72 mM to yield attraction of counterion. The micellar sizes increased with increase in concentration of CTAB (higher than 4.02 mM) to generate micron-sized micelles. The distribution of micellar sizes was used to estimate the molecular weight cutoff of membrane used in the MEUF process. As chromium was added into aqueous CTAB solution, the chromate was dominant and bound on the micellar surface instead of Br-. Moreover, the presence of micelle formed a gel-layer to slightly shrink the membrane pore, therefore, UF membrane of 30k Da molecular weight cutoff (pore size≈7.9 nm) was selected in the MEUF process to achieve the removal efficiency of Cr(VI) higher than 95%.

Novelties of combustion synthesized titania ultrafiltration membrane in efficient removal of methylene blue dye from aqueous effluent

In this study, titania nanoparticles were synthesized by combustion and used to make ultrafiltration membrane. Characteristics of titania membranes such as textural evaluation, surface morphology, pure water permeability and protein rejection were investigated. Titania membrane sintered at 450 °C showed pure water permeability 11 × 10−2 L h−1 m−2 kPa−1 and 76% protein rejection. The membrane presented good water flux and retention properties with regards to protein and methylene blue dye. Ultrafiltration process was operated at lower pressure (100 kPa) and showed 99% removal of methylene blue using adsorptive micellar flocculation at sodium dodecyl sulfate concentration below its critical micellar concentration. Ferric chloride was used as the coagulant. The method of making titania membrane and its use are new. These studies can be extended to other dyes and pollutants.