Photocatalytic membrane reactor for simultaneous separation and photoreduction of CO2 to methanol

The two-layer photocatalytic membranes fabricated from a porous polyethersulfone-TiO2 (PES-TiO2) as a photocatalytic layer and a thin nonporous layer of poly-ether-block-amide (PEBAX-1657) as a selective layer were used to solve the problems of slurry photocatalyst systems and substitute a single operating unit for simultaneous separation and conversion of CO2. The photocatalytic features, hydrophilicity, surface chemistry, and morphology of photocatalytic membranes were characterized by Ultraviolet-visible (UV-visible), contact angle, Attenuated Total Reflection-Fourier Transforms Infrared (ATR-FTIR), and (Scanning Electron Microscopy) SEM, respectively. Compared with membrane without any nanoparticle, the separation performance of nanocomposite membranes using the gas mixture (containing CO2 and CH4 with the molar ratio of 1:4), as the feed, was slightly increased by adding TiO2 content in the support layer. The effects of TiO2 nanoparticle contents, water flow rates as well as light powers on the photoreduction of CO2 to methanol in terms of methanol concentration and production yield were investigated under Ultraviolet (UV) irradiation. As depicted by UV-vis analysis, the UV irradiation absorption of photocatalytic membranes increased with increasing of TiO2 contents. Moreover, the ATR-FTIR results confirmed the presence of TiO2 nanoparticle on the photocatalytic membrane surface. The photocatalytic performance revealed that utilizing simultaneous separation and conversion for CO2 photoreduction in the presence of water represented the high methanol production yield about 697 mu mol/g(cat).h at 5 wt. % of TiO2 nanoparticle contents, 3 mL/min of water flow rate and 8.84 W/cm(2) of light power. Meanwhile, the possible mechanism of the TiO2 photocatalytic performance for CO2 photoreduction to methanol was clarified. In addition, it was confirmed that the photocatalytic membranes were efficient until after four runs. Therefore, the utilization of photocatalytic membrane is an effective approach to improve the beneficial combination of photocatalytic process and membrane technology, simultaneously.

Automated summary

In this study, dual-layer photocatalytic membranes were successfully utilized to address the issues of slurry photocatalyst systems and achieve simultaneous separation and conversion of CO2. The addition of TiO2 nanoparticles improved the separation performance of photocatalytic membranes towards CO2. The photocatalytic membranes exhibited high methanol production yield under UV irradiation.