ABSTRACT
Due to its environmental friendliness and biodegradable ability, the enzymatic decolorization of azo dyes is the best option. However, the free enzyme suffers from various limitations, including poor stability, no repeatable use, and a high expense, which is the key drawback for its practical use. In this analysis, the laccase enzyme was immobilized in mesoporous silica coated magnetic multiwalled carbon nanotubes (Fe3O4-MWCNTs@SiO2) by a glutaraldehyde cross-linker to create an easily separable and stable enzyme. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the as-synthesized Fe3O4-MWCNTs@SiO2. Laccase immobilized in Fe3O4-MWCNTs@SiO2 showed a good improvement in temperature, pH, and storage stability. Moreover, the operational stability of the biocatalyst was improved, retaining 87% of its original activity even after 10 cycles of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) oxidation. The biocatalysts were applied for the decolorization of selected azo dyes without a mediator, and up to 99% of Eriochrome Black T (EBT), 98% of Acid Red 88 (AR 88), and 66% of Reactive Black 5 (RB5) were decolorized. Based on these properties, the biocatalysts can be potentially utilized in various environmental and industrial applications.
ABSTRACT
Although loose nanofiltration membranes have been extensively studied for dye desalination, high-throughput membranes with antifouling and antibacterial properties are still highly needed. In this study, a zwitterion-modified molybdenum disulfide (MoS2) dual-layer loose nanofiltration membrane was prepared with the integration of antibacterial, antifouling, and high-flux properties. To be specific, MoS2 nanosheets were loaded on a polyacrylonitrile ultrafiltration membrane through pressure-assisted self-assembly. Then, poly (sulfobetaine methacrylate) (PSBMA) was coated on the surface of the MoS2 membrane via a simple polydopamine (PDA)-assisted one-step codeposition to prepare PSBMA/PDA/MoS2 nanofiltration membranes. Elemental and morphological analyses confirmed the formation of the MoS2 layer and PSBMA/PDA coating. In addition, the effect of the PSBMA amount and codeposition time on surface properties and membrane performances was investigated. Under optimum conditions, the as-prepared membrane showed excellent water permeance of 262 LMH/bar with good dye rejection (99.8% for methylene blue) and salt permeability, as well as excellent antifouling and antibacterial properties benefiting from the synergy of PSBMA/PDA coating layers and MoS2 layers.
ABSTRACT
The nanosized UiO-66-NH2 metal-organic framework (MOF) material was synthesized and modified by palmitoyl chloride to enhance the dispersibility and restrain the aggregation of MOF particles in the organic phase. Then the above nanomaterial was introduced into interfacial polymerization to prepare thin film nanocomposite (TFN) nanofiltration membranes. The prepared membranes displayed "ridge-valley" shaped Turing structure surface morphology with membrane thickness around 380 nm. The FE-SEM, ATR-FTIR and XPS characterization showed the polyamide layer was fabricated on the substrate surface. The TFN membranes showed higher hydrophobicity, zeta potential and roughness than TFC membranes. Due to the introduction of MOF and the formation of MOF/polyamide interfacial passageways, the TFN membranes showed higher water permeability but slightly lower rejection properties than TFC membranes. Compared with the TFN membranes prepared from pristine UiO-66 and UiO-66-NH2, the TFN membrane prepared from modified UiO-66-NH2 showed better rejection properties because of its superior dispersibility in the organic phase.
ABSTRACT
Inorganic nanofiltration membranes with high flux are urgently needed in water purification processes. Herein, polydopamine (PDA)-modified layer-stacked molybdenum disulfide (MoS2) nanofiltration membranes (NFMs) were fabricated via a pressure-assisted self-assembly process. The separation performance of the as-prepared membranes with various MoS2 loadings at different dopamine polymerization times was evaluated. The pure water permeance of PDA-modified MoS2 NFMs, with MoS2 loading of 0.1103 mg/cm2 at 4 h modification, could reach 135.3 LMH/bar. The rejection toward methylene blue could reach 100% with molecular weight cutoff approximately 671 Da and a high permeability of salts. Furthermore, the resultant membrane also exhibited a satisfactory long-term stability toward dye solution and antifouling property toward bovine serum albumin. This work may give inspiration to the development of inorganic membranes with high performance, especially high pure water permeance, for water-related processes.