Comparison of Photocatalytic Membrane Reactor Types for the Degradation of an Organic Molecule by TiO₂-Coated PES Membrane

Photocatalytic membrane reactors with different configurations (design, flow modes and light sources) have been widely applied for pollutant removal. A thorough understanding of the contribution of reactor design to performance is required to be able to compare photocatalytic materials. Reactors with different flow designs are implemented for process efficiency comparisons. Several figures-of-merit, namely adapted space-time yield (STY) and photocatalytic space-time yield (PSTY), specific energy consumption (SEC) and degradation rate constants, were used to assess the performance of batch, flow-along and flow-through reactors. A fair comparison of reactor performance, considering throughput together with energy efficiency and photocatalytic activity, was only possible with the modified PSTY. When comparing the three reactors at the example of methylene blue (MB) degradation under LED irradiation, flow-through proved to be the most efficient design. PSTY1/PSTY2 values were approximately 10 times higher than both the batch and flow-along processes. The highest activity of such a reactor is attributed to its unique flow design which allowed the reaction to take place not only on the outer surface of the membrane but also within its pores. The enhancement of the mass transfer when flowing in a narrow space (220 nm in flow-through) contributes to an additional MB removal. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Improved CO2/CH4 Separation Properties of Cellulose Triacetate Mixed–Matrix Membranes with CeO2@GO Hybrid Fillers

The study of the effects associated with the compatibility of the components of the hybrid filler with polymer matrix, which ultimately decide on achieving mixed matrix membranes (MMMs) with better gas separation properties, is essential. Herein, a facile solution casting process of simple incorporating CeO2@GO hybrid inorganic filler material is implemented. Significant improvements in material and physico-chemical properties of the synthesized membranes were observed by SEM, XRD, TGA, and stress-strain measurements. Usage of graphene oxide (GO) with polar groups on the surface enabled forming bonds with ceria (CeO2) nanoparticles and CTA polymer and provided the homogeneous dispersion of the nanofillers in the hybrid MMMs. Moreover, increasing GO loading concentration enhanced both gas permeation in MMMs and CO2 gas uptakes. The best performance was achieved by the membrane containing 7 wt.% of GO with CO2 permeability of 10.14 Barrer and CO2/CH4 selectivity 50.7. This increase in selectivity is almost fifteen folds higher than the CTA-CeO2 membrane sample, suggesting the detrimental effect of GO for enhancing the selectivity property of the MMMs. Hence, a favorable synergistic effect of CeO2@GO hybrid fillers on gas separation performance is observed, propounding the efficient and feasible strategy of using hybrid fillers in the membrane for the potential biogas upgrading process

CO2/CH4 and H2/CH4 Gas Separation Performance of CTA-TNT@CNT Hybrid Mixed Matrix Membranes

This study explored the underlying synergy between titanium dioxide nanotube (TNT) and carbon nanotube (CNT) hybrid fillers in cellulose triacetate (CTA)-based mixed matrix membranes (MMMs) for natural gas purification. The CNT@TNT hybrid nanofillers were blended with CTA polymer and cast as a thin film by a facile casting technique, after which they were used for single gas separation. The hybrid filler-based membrane depicted a higher CO2 uptake affinity than the single filler (CNT/TNT)-based membrane. The gas separation results indicate that the hybrid fillers (TNT@CNT) are strongly selective for CO2 over CH4 and H2 over CH4. The increment in the CO2/CH4 and H2/CH4 selectivities compared to the pristine CTA membrane was 42.98 from 25.08 and 48.43 from 36.58, respectively. Similarly, the CO2 and H2 permeability of the CTA-TNT@CNT membrane increased by six- and five-fold, respectively, compared to the pristine CTA membrane. Such significant improvements in CO2/CH4 and H2/CH4 separation performance and thermal and mechanical properties suggest a feasible and practical approach for potential biogas upgrading and natural gas purification

Efficient inactivation of Staphylococcus aureus by silver and copper loaded photocatalytic titanate nanotubes

One dimensional titanate nanotubes (TNTs) were synthesized by microwave assisted alkaline hydrothermal process. The process was followed by UV-photodeposition of Ag and Cu on the surface of TNTs to enhance the photocatalytic activity in visible light spectrum. The loading of Ag and Cu (single and combination mode) offered a new insight to inactivate multi-drug resistant micro-organisms. The antibacterial properties of these samples were studied on Gram positive bacteria, Staphylococcus aureus (S. aureus) using well diffusion method. The TNTs with Ag and Cu loading showed a clear zone of inhibition after overnight incubation of S. aureus. The bacterial inactivation efficiency of nanoparticles in the visible light was further analyzed by kill kinetics. TNTs with Ag and/or Cu loading showed a significant reduction in bacterial growth. Cu co-loaded with Ag sample showed the highest inactivation efficiency within 90 min of visible light irradiation. To elucidate the mechanism of bactericidal properties of samples under visible light irradiation, the formation of reactive oxygen species (ROS), particularly, superoxide radical anion was determined by nitro blue tetrazolium (NBT) assay and the protein degradation by each samples were measured. Based on overall results, it was observed that the Cu co-loaded with Ag on TNTs samples were found to be more effective as compared to either Ag or Cu loaded TNTs. It provides new avenues for utilizing the combination of Cu and Ag for enhancing the antimicrobial efficacies for different nanoparticles. Keywords: Titante nanotubes, Staphylococcus aureus, Antibacterial, Photocatalytic inactivation, Reactive oxygen specie

Cellulose Triacetate-Based Mixed-Matrix Membranes with MXene 2D Filler—CO2/CH4 Separation Performance and Comparison with TiO2-Based 1D and 0D Fillers

Mixed-matrix membranes (MMMs) possess the unique properties and inherent characteristics of their component polymer and inorganic fillers, or other possible types of additives. However, the successful fabrication of compact and defect-free MMMs with a homogeneous filler distribution poses a major challenge, due to poor filler/polymer compatibility. In this study, we use two-dimensional multi-layered Ti3C2Tx MXene nanofillers to improve the compatibility and CO2/CH4 separation performance of cellulose triacetate (CTA)-based MMMs. CTA-based MMMs with TiO2-based 1D (nanotubes) and 0D (nanofillers) additives were also fabricated and tested for comparison. The high thermal stability, compact homogeneous structure, and stable long-term CO2/CH4 separation performance of the CTA-2D samples suggest the potential application of the membrane in bio/natural gas separation. The best results were obtained for the CTA-2D sample with a loading of 3 wt.%, which exhibited a 5-fold increase in CO2 permeability and 2-fold increase in CO2/CH4 selectivity, compared with the pristine CTA membrane, approaching the state-of-the-art Robeson 2008 upper bound. The dimensional (shape) effect on separation performance was determined as 2D > 1D > 0D. The use of lamellar stacked MXene with abundant surface-terminating groups not only prevents the aggregation of particles but also enhances the CO2 adsorption properties and provides additional transport channels, resulting in improved CO2 permeability and CO2/CH4 selectivity

Understanding Mechanism of Photocatalytic Microbial Decontamination of Environmental Wastewater

Several photocatalytic nanoparticles are synthesized and studied for potential application for the degradation of organic and biological wastes. Although these materials degrade organic compounds by advance oxidation process, the exact mechanisms of microbial decontamination remains partially known. Understanding the real mechanisms of these materials for microbial cell death and growth inhibition helps to fabricate more efficient semiconductor photocatalyst for large-scale decontamination of environmental wastewater or industries and hospitals/biomedical labs generating highly pathogenic bacteria and toxic molecules containing liquid waste by designing a reactor. Recent studies on microbial decontamination by photocatalytic nanoparticles and their possible mechanisms of action is highlighted with examples in this mini review