Li-guang Wu

Enhanced Performance of Polyurethane Hybrid Membranes for CO2 Separation by Incorporating Graphene Oxide: The Relationship between Membrane Performance and Morphology of Graphene Oxide

Polyurethane hybrid membranes containing graphene oxide (GO) with different morphologies were prepared by in situ polymerization. The separation of CO2/N2 gas mixtures was studied using these novel membranes. The results from the morphology characterization of GO samples indicated that the oxidation process in the improved Hummers method introduced oxygenated functional groups into graphite, making graphite powder exfoliate into GO nanosheets. The surface defects on the GO sheets increased when oxidation increased due to the introduction of more oxygenated functional groups. Both the increase in oxygenated functional groups on the GO surface and the decrease in the number of GO layers leads to a better distribution of GO in the polymer matrix, increasing thermal stability and gas separation performance of membranes. The addition of excess oxidant destroyed the structure of GO sheets and forms structural defects, which depressed the separation performance of membranes. The hybrid membranes containing well-distributed GO showed higher permeability and permeability selectivity for the CO2. The formation of GO aggregates in the hybrid membranes depressed the membrane performance at a high content of GO.

Enhanced photocatalytic activity for degrading phenol in seawater by TiO2-based catalysts under weak light irradiation

The seawater system is a typical salt water system. A catalyst should overcome the disturbance from the salt ions for an efficient photodegradation of organic pollutants in the seawater system. Commercial photocatalysts (P25) and La3+-doped SiO2–TiO2 prepared using adsorbed-layer nanoreactor synthesis (ALNS) were first used for photodegrading different initial concentrations of phenol in seawater under weak UV light irradiation. The weak adsorption capacities for phenol and the hydrophilic surfaces of the two photocatalysts could not overcome the disturbance of salt ions and thus showed low photocatalytic activities. Based on this, graphene oxide (GO) was used as a support to prepare TiO2 and La3+-doped TiO2 using ALNS. The solvothermal treatment with alcohol was used as a solvent for both TiO2 crystallization and GO reduction. Results showed that TiO2 nanoparticles with sizes <10 nm formed and distributed homogeneously on the reduced GO surface. The small size of the TiO2 particles and the decreased oxygenated functional groups on the GO surface both caused high separation efficiency of the photogenerated charge carriers, thereby increasing the photodegradation performance. The strong phenol adsorption of the photocatalyst was efficient enough to overcome the interference of salt ions and enhance the photodegradation efficiency in seawater. The activities of the two Red–GO–TiO2 catalysts were more than twice those of P25 and La3+-doped SiO2–TiO2. La3+ doping caused mixed crystals to form and increased the shallow trapping sites for charge carriers. Therefore, La3+ doping increases the photocatalytic activity of Red–GO–TiO2.

Fabrication of Polyimide Membrane Incorporated with Functional Graphene Oxide for CO2 Separation: The Effects of GO Surface Modification on Membrane Performance

Two kinds of isocyanate were used to modify graphene oxide (GO) samples. Then, polyimide (PI) hybrid membranes containing GO and modified GO were prepared by in situ polymerization. The permeation of CO2 and N2 was studied using these novel membranes. The morphology experiments showed that the isocyanate groups were successfully grafted on the surface of GO by replacement of the oxygen-containing functional groups. After modification, the surface polarity of the GO increased, and more defect structures were introduced into the GO surface. This resulted in a good distribution of more modified GO samples in the PI polymer matrix. Thus, the PI hybrid membranes incorporated by modified GO samples showed a high gas permeability and ideal selectivity of membranes. In addition, enhancement of the selectivity due to the solubility of CO2 played a major role in the increase in the separation performance of the hybrid membranes for CO2, although the diffusion coefficients for CO2 also increased. Both the higher condensability and the strong affinity between CO2 molecules and GO in the polymer matrix caused an enhancement of the solubility selectivity higher than the diffusion selectivity after GO surface modification.

Novel hybrid membranes by incorporating SiO2 nanoparticles using in situ microemulsion polymerization: preparation, characterization and enhancement in the performance for CO2/N2

SiO2 nanoparticles were synthesized in a water-in-oil microemulsion using a triblock copolymer as the surfactant and methyl methacrylate as the oil phase. Then, SiO2/poly(methyl methacrylate) (PMMA) hybrid membranes were prepared by in situ microemulsion polymerization. The separation of CO2/N2 gas mixtures was studied using these novel membranes. Both the gas permeability and separation performance of the hybrid membranes first increased and then decreased with SiO2 content. When the SiO2 content was 4.0 wt%, the CO2 permeability and permeability selectivity of the membranes for CO2/N2 gas mixtures were both at a maximum. For comparison, two commercially available SiO2 nanoparticle materials were also used to synthesize SiO2/PMMA membranes by solution polymerization. The particle size of SiO2 in the microemulsion was close to the two commercially available SiO2 nanoparticle materials. The SiO2 nanoparticles formed in the microemulsion were distributed more homogeneously in the membranes than the commercially available nanoparticles because of the protection by the water droplets. Moreover, the SiO2 nanoparticles formed in the water droplets and reverse microemulsion had a strong polar surface. Therefore, the SiO2/PMMA hybrid membrane formed by the in situ microemulsion polymerization had better performance than the hybrid membranes made with commercially available SiO2 nanoparticles.