Spray assisted layer-by-layer assembled one-bilayer polyelectrolyte reverse osmosis membranes

Effect of Saccharides Coating on Antibacterial Potential and Drug Loading and Releasing Capability of Plasma Treated Polylactic Acid Films

More than half of the hospital-associated infections worldwide are related to the adhesion of bacteria cells to biomedical devices and implants. To prevent these infections, it is crucial to modify biomaterial surfaces to develop the antibacterial property. In this study, chitosan (CS) and chondroitin sulfate (ChS) were chosen as antibacterial coating materials on polylactic acid (PLA) surfaces. Plasma-treated PLA surfaces were coated with CS either direct coating method or the carbodiimide coupling method. As a next step for the combined saccharide coating, CS grafted samples were immersed in ChS solution, which resulted in the polyelectrolyte complex (PEC) formation. Also in this experiment, to test the drug loading and releasing efficiency of the thin film coatings, CS grafted samples were immersed into lomefloxacin-containing ChS solution. The successful modifications were confirmed by elemental composition analysis (XPS), surface topography images (SEM), and hydrophilicity change (contact angle measurements). The carbodiimide coupling resulted in higher CS grafting on the PLA surface. The coatings with the PEC formation between CS-ChS showed improved activity against the bacteria strains than the separate coatings. Moreover, these interactions increased the lomefloxacin amount adhered to the film coatings and extended the drug release profile. Finally, the zone of inhibition test confirmed that the CS-ChS coating showed a contact killing mechanism while drug-loaded films have a dual killing mechanism, which includes contact, and release killing.

Coffee Grounds-Doped Alginate Porous Materials for Efficient Solar Steam Generation

Solar steam generation (SSG) devices have emerged as one of the promising technologies for seawater desalination to meet the worldwide demand for clean water. Herein, we fabricated a new monolithic SSG system derived from waste coffee grounds (CG) through a simple carbonization followed by a freeze-drying process (named as CCGA). The as-prepared CCGA possesses a porous structure with superhydrophilic, abundant porosity (81.7%); low thermal conductivity (0.129 W m^-1 K^-1) in a wet state; low apparent density (25 mg cm^-3); and broad sunlight absorption in a wet state (ca. 93%). The combination of its carbon nature and abundant porous structure endowed barrier-free water transmission channels, a self-floating property, and a superb photothermal conversion performance to the SSG. The temperature of the CCGA's upper surface can reach up to 42.6 °C under 1 sun irradiation, and for pure water, the evaporation rate of CCGA can be up to 1.486 kg m^-2 h^-1, corresponding to a good photothermal conversion efficiency of 86.96%. It also exhibits an excellent desalination capability; e.g., the photothermal conversion efficiency of CCGA in NaCl (20 wt %) brine is measured to be 75.77% under 1 sun irradiation, and the fresh water obtained from artificial seawater can achieve the WHO's standard for domestic water. With the advantages of low cost and a simple preparation process, such biomass-based CCGA materials may have great potential as an efficient SSG device for seawater desalination.

Versatile Janus Composite Nonwoven Solar Absorbers with Salt Resistance for Efficient Wastewater Purification and Desalination

Solar steam generation is an efficient way of harvesting solar energy for water purification. Developing a versatile solar absorber with salt resistance and the capability to purify an oil-in-water emulsion is a grand challenge. Herein, a polypropylene (PP) nonwoven fabric-based photothermal absorber is fabricated by the combination of carbon nanotubes (CNTs), polypyrrole (PPy), and a fluorinated hydrophobic coating in a layer-by-layer approach. The specially designed architecture displays a hierarchical microstructure and Janus wetting properties, facilitating solar absorption and heat generation on the evaporation surface, and can effectively prevent salt crystallization. The water layer formed on the superhydrophilic/underwater superoleophobic bottom surface could repel oil droplets and form a channel to advect concentrated salt back into bulk water, which enabled high purity separation of an oil-in-water emulsion and continuous desalinization of seawater without the reduction of the evaporation rate. As a result, the solar absorber can achieve a remarkable evaporation rate of 1.61 kg m^-2 h^-1 and an energy efficiency of 91.2% under 1 sun irradiation and shows extraordinary performance in the purification of contaminated wastewater (over 99.8% purity). The strategy proposed provides a pathway for developing versatile high-performance solar absorbers for the sustainable treatment of saline water, wastewater, and oil-containing water.

A Comprehensive Review on Membrane Fouling: Mathematical Modelling, Prediction, Diagnosis, and Mitigation

Membrane-based separation has gained increased popularity over the past few decades, particularly reverse osmosis (RO). A major impediment to the improved performance of membrane separation processes, in general, is membrane fouling. Fouling has detrimental effects on the membrane’s performance and integrity, as the deposition and accumulation of foulants on its surface and/or within its pores leads to a decline in the permeate flux, deterioration of selectivity, and permeability, as well as a significantly reduced lifespan. Several factors influence the fouling-propensity of a membrane, such as surface morphology, roughness, hydrophobicity, and material of fabrication. Generally, fouling can be categorized into particulate, organic, inorganic, and biofouling. Efficient prediction techniques and diagnostics are integral for strategizing control, management, and mitigation interventions to minimize the damage of fouling occurrences in the membranes. To improve the antifouling characteristics of RO membranes, surface enhancements by different chemical and physical means have been extensively sought after. Moreover, research efforts have been directed towards synthesizing membranes using novel materials that would improve their antifouling performance. This paper presents a review of the different membrane fouling types, fouling-inducing factors, predictive methods, diagnostic techniques, and mitigation strategies, with a special focus on RO membrane fouling.

Three-dimensional self-floating foam composite impregnated with porous carbon and polyaniline for solar steam generation

A promising approach to resolving insufficient freshwater resources is utilizing solar energy for steam generation. Although various types of photothermal conversion materials have been developed, there are still some obstacles, such as complicated system structure fabrication and low energy utilization, that severely hinder their practical application. Herein, we designed and produced a self-floating porous carbon/polyaniline foam (PCPF) evaporator via impregnating melamine foam with porous carbon generated following the bottom-up pyrolytic method and polyaniline, followed by thermal treatment, for efficient solar steam generation. The PCPF obtained with a porous carbon (PC) to polyaniline (PAN) mass ratio of 3:5 (PCPF-3) exhibited a rich pore structure, good hydrophilicity, low thermal conductivity (0.0413 W m^-1 K^-1), and excellent light absorption (96.1%). Our results show that, without additional thermal insulators, the evaporation rate of PCPF-3 reached 1.496 kg m^-2 h^-1, and the photothermal conversion efficiency reached 87.3% under one sun irradiation. Furthermore, it also exhibited good durability and desalination performance. This type of environmentally friendly, low-cost, and stable photothermal conversion material could be used in water treatment and seawater desalination.