Enhanced antifouling and antimicrobial thin film nanocomposite membranes with incorporation of Palygorskite/titanium dioxide hybrid material

Dencichine/palygorskite nanocomposite incorporated chitosan/polyvinylpyrrolidone film for accelerating wound hemostasis

The development of efficient, safe, environmentally friendly, and user-friendly hemostatic dressings remains a great challenge for researchers. A variety of clay minerals and plant extracts have garnered considerable attention due to their outstanding hemostatic efficacy and favorable biosafety. In this study, a facile solution casting strategy was employed to prepare nanocomposite films by incorporating natural nanorod-like palygorskite (Pal) and herb-derived hemostat dencichine (DC) based on chitosan and polyvinylpyrrolidone. The dynamic blood clotting index demonstrated that the nanocomposite film with a DC addition of 1.0 wt% exhibited significantly superior hemostatic properties compared to both pure DC powder or commercial hemostatic agent Yunnan Baiyao. This improvement was primarily attributed to proper blood affinity, increased porosity, enhanced adhesion of platelets and erythrocytes, as well as the accelerated activation of coagulation factors and platelets. Under the synergistic effect of Pal and DC, the nanocomposite film displayed suitable tensile strength (20.58 MPa) and elongation at break (47.29 %), which may be due to the strong intermolecular hydrogen bonding and electrostatic interaction between Pal/DC and macropolymers. Notably, the nanocomposite film exhibited remarkable antibacterial effectiveness and desirable cytocompatibility, as well as the capability of promoting wound healing in vitro. Taken together, the nanocomposite film synergized with Pal and DC is expected to be an efficacious and suitable wound dressing.

Nano-enabled antimicrobial thin films: design and mechanism of action

Antimicrobial thin films are types of protective coatings that are applied to surfaces such as medical devices, food packaging materials, water-resistant coatings, and other systems. These films prevent and reduce the spread of microbial organisms, including bacteria, fungi, and viruses. Antimicrobial thin films can be prepared from a variety of nanostructured materials including metal nanoparticles, metal oxides, plant materials, enzymes, bacteriocins and polymers. Their antimicrobial mechanism varies mostly based on the types of active agents from which the film is made of. Antimicrobial thin films are becoming increasingly popular microbial treatment methods due to their advantages such as enhanced stability, reduced toxicity levels, extended effectiveness over time and broad spectrum antimicrobial action without side effects on human health or the environment. This popularity and enhanced performance is mainly due to the extended possibility of film designs. Thin films offer convenient formulation methods which makes them suitable for commercial practices aiming at high turnover rates along with residential applications requiring frequent application cycles. This review focuses on recent developments in the possible processing methods and design approaches for assembling the various types of antimicrobial materials into nanostructured thin film-based delivery systems, along with mechanisms of action against microbes.

Synthesis and characterization of TiO2 nanoparticles combined with geraniol and their synergistic antibacterial activity

BACKGROUND

The emergence of antibiotic resistance in pathogenic bacteria has become a global threat, encouraging the adoption of efficient and effective alternatives to conventional antibiotics and promoting their use as replacements. Titanium dioxide nanoparticles (TiO₂ NPs) have been reported to exhibit antibacterial properties. In this study, we synthesized and characterized TiO₂ NPs in anatase and rutile forms with surface modification by geraniol (GER).

RESULTS

The crystallinity and morphology of modified TiO₂ NPs were analyzed by UV/Vis spectrophotometry, X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) with elemental mapping (EDS). The antimicrobial activity of TiO₂ NPs with geraniol was assessed against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and Escherichia coli. The minimum inhibitory concentration (MIC) values of modified NPs ranged from 0.25 to 1.0 mg/ml against all bacterial strains, and the live dead assay and fractional inhibitory concentration (FIC) supported the antibacterial properties of TiO₂ NPs with GER. Moreover, TiO₂ NPs with GER also showed a significant decrease in the biofilm thickness of MRSA.

CONCLUSIONS

Our results suggest that TiO₂ NPs with GER offer a promising alternative to antibiotics, particularly for controlling antibiotic-resistant strains. The surface modification of TiO₂ NPs by geraniol resulted in enhanced antibacterial properties against multiple bacterial strains, including antibiotic-resistant MRSA. The potential applications of modified TiO₂ NPs in the biomedical and environmental fields warrant further investigation.

Silk Nanofibril-Palygorskite Composite Membranes for Efficient Removal of Anionic Dyes

To develop membrane materials with good performance for water purification that are green and low cost, this work reports an organic-inorganic composite membrane composed of silk nanofibrils (SNFs) and palygorskite (PGS). To improve the stability of the the composite membrane, genipin was used as a crosslinking agent to induce the conformational transition of SNF chains from random coils to β-sheets, reducing the swelling and hydrolysis of the membrane. The separation performance can be adjusted by tailoring the component ratio of the nanomaterial. The results showed that these membranes can effectively remove anionic dyes from water, and they exhibit excellent water permeability. The SNF-based membrane had strong mechanical and separation properties, and the PGS could tune the structure of composite membranes to enhance their permeability, so this green composite membrane has good prospects in water treatment and purification applications.

Titanium dioxide nanoparticles: Recent progress in antimicrobial applications

For decades, the antimicrobial applications of nanoparticles (NPs) have attracted the attention of scientists as a strategy for controlling the ever-increasing threat of multidrug-resistant microorganisms. The photo-induced antimicrobial properties of titanium dioxide (TiO₂ ) NPs by ultraviolet (UV) light are well known. This review elaborates on the modern methods and antimicrobial mechanisms of TiO₂ NPs and their modifications to better understand and utilize their potential in various biomedical applications. Additional compounds can be grafted onto TiO₂ nanomaterial, leading to hybrid metallic or non-metallic materials. To improve the antimicrobial properties, many approaches involving TiO₂ have been tested. The results of selected studies from the past few years covering the most recent trends in this field are discussed in this review. There is extensive evidence to show that TiO₂ NPs can exhibit certain antimicrobial features with disputable roles of UV light. Hence, they are effective in treating bacterial infections, although the majority of these conclusions came from in vitro studies and in the presence of some additional nanomaterials. The methods of evaluation varied depending on the nature of the research while researchers incorporated different techniques, including determining the minimum inhibitory concentration, cell count, and using disk and well diffusion methods, with a noticeable indication that cell count was the most and dominant criterion used to evaluate the antimicrobial activity. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Metal-Organic Framework-Based Materials for Adsorption and Detection of Uranium(VI) from Aqueous Solution

The steady supply of uranium resources and the reduction or elimination of the ecological and human health hazards of wastewater containing uranium make the recovery and detection of uranium in water greatly important. Thus, the development of effective adsorbents and sensors has received growing attention. Metal-organic frameworks (MOFs) possessing fascinating characteristics such as high surface area, high porosity, adjustable pore size, and luminescence have been widely used for either uranium adsorption or sensing. Now pertinent research has transited slowly into simultaneous uranium adsorption and detection. In this review, the progress on the research of MOF-based materials used for both adsorption and detection of uranium in water is first summarized. The adsorption mechanisms between uranium species in aqueous solution and MOF-based materials are elaborated by macroscopic batch experiments combined with microscopic spectral technology. Moreover, the application of MOF-based materials as uranium sensors is focused on their typical structures, sensing mechanisms, and the representative examples. Furthermore, the bifunctional MOF-based materials used for simultaneous detection and adsorption of U(VI) from aqueous solution are introduced. Finally, we also discuss the challenges and perspectives of MOF-based materials for uranium adsorption and detection to provide a useful inspiration and significant reference for further developing better adsorbents and sensors for uranium containment and detection.

Simple preparation of novel photochromic polyvinyl alcohol/carboxymethyl cellulose security barcode incorporated with lanthanide-doped aluminate for anticounterfeiting applications

Forgery and low-quality products pose a danger to the society. Therefore, there are increasing demands for the production of easy to recognize and difficult to copy anti-counterfeiting materials. Products with smart photochromic and fluorescent properties can change color and emission spectra responding to a light source. In this context, we devised a straightforward preparation of luminescent polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) nanocomposite to function as a transparent labeling film. The lanthanide-doped aluminate (LdA) was prepared in the nanoparticle form to indicate diameters of 35-115 nm. Different ratios of the lanthanide-doped aluminate (LdA) were physically dispersed in the PVA/CMC nanocomposite label film to provide photochromic, ultraviolet protection, antimicrobial activity and hydrophobic properties. Fluorescence peaks were detected at 365 and 519 nm to indicate a color change to green. As a result of increasing the phosphor ratio, improved superhydrophobic activity was achieved as the contact angle increased from 126.1° to 146.0° without affecting the film original physical and mechanical properties. Both UV protection and antibacterial activity were also investigated. The films showed quick and reversible photochromic response without fatigue. The current strategy reported the development of photochromic smart label that is transparent, cost-effective and flexible. As a result, numerous anticounterfeiting products can benefit from the current label for a better market. LdA-loaded PVA/CMC films demonstrated antibacterial activity between poor, good, very good and outstanding as the percentage of LdA in the film matrix increased. The current film can be applied as a transparent photochromic security barcode for anticounterfeiting applications and smart packaging.

Antibiotic Resistance in the Drinking Water: Old and New Strategies to Remove Antibiotics, Resistant Bacteria, and Resistance Genes

Bacterial resistance is a naturally occurring process. However, bacterial antibiotic resistance has emerged as a major public health problem in recent years. The accumulation of antibiotics in the environment, including in wastewaters and drinking water, has contributed to the development of antibiotic resistant bacteria and the dissemination of antibiotic resistance genes (ARGs). Such can be justified by the growing consumption of antibiotics and their inadequate elimination. The conventional water treatments are ineffective in promoting the complete elimination of antibiotics and bacteria, mainly in removing ARGs. Therefore, ARGs can be horizontally transferred to other microorganisms within the aquatic environment, thus promoting the dissemination of antibiotic resistance. In this review, we discuss the efficiency of conventional water treatment processes in removing agents that can spread/stimulate the development of antibiotic resistance and the promising strategies for water remediation, mainly those based on nanotechnology and microalgae. Despite the potential of some of these approaches, the elimination of ARGs remains a challenge that requires further research. Moreover, the development of new processes must avoid the release of new contaminants for the environment, such as the chemicals resulting from nanomaterials synthesis, and consider the utilization of green and eco-friendly alternatives such as biogenic nanomaterials and microalgae-based technologies.

Photocatalytic degradation of Novacron blue and Novacron yellow textile dyes by the TiO2/palygorskite nanocomposite

The photocatalytic discoloration of industrial dyes, Novacron blue (NB) and Novacron yellow (NY), was investigated using composites based on TiO₂ and natural palygorskite (Pal-Ti10 and Pal-Ti30). The method consisted of synthesizing the composites starting from a physical mixture of TiO₂ and natural palygorskite in the presence of alcohol, for impregnation through calcination under conditions of temperature equal to 450 °C and atmospheric air. The characterization techniques used in this work were FTIR, XRD, XRF, SEM, particle size analysis and zeta potential. The photocatalysis for the NB dye was investigated through the application of a factorial 2⁴ experimental design, aiming at the best experimental conditions and finally applying them in another NY industrial dye. The investigated concentrations of NB were 10 ppm and 30 ppm, the composites were synthesized using 10 and 30% (p/p) of titanium dioxide in palygorskite, the two pH values were 2.0 and 6.0 and the light intensities 9 and 18 W were used. Tests performed at pH 2.0, Pal-Ti30 composite, power 18 W and 10 ppm of dye showed 100% color removal of both dyes in 90 min. The bleaching process followed the pseudo-first order kinetic model, and the apparent constants (K_app) were 0.0216 min^-1 and 0.0193 min^-1 for NB and NY dyes, respectively. The results of total organic carbon (TOC) showed mineralization of 61.70% and 58.06% for NB and NY, respectively, in 90 min of treatment, and the by-products were detected by GC-MS.

Nanofiltration for drinking water treatment: a review

In recent decades, nanofiltration (NF) is considered as a promising separation technique to produce drinking water from different types of water source. In this paper, we comprehensively reviewed the progress of NF-based drinking water treatment, through summarizing the development of materials/fabrication and applications of NF membranes in various scenarios including surface water treatment, groundwater treatment, water reuse, brackish water treatment, and point of use applications. We not only summarized the removal of target major pollutants (e.g., hardness, pathogen, and natural organic matter), but also paid attention to the removal of micropollutants of major concern (e.g., disinfection byproducts, per- and polyfluoroalkyl substances, and arsenic). We highlighted that, for different applications, fit-for-purpose design is needed to improve the separation capability for target compounds of NF membranes in addition to their removal of salts. Outlook and perspectives on membrane fouling control, chlorine resistance, integrity, and selectivity are also discussed to provide potential insights for future development of high-efficiency NF membranes for stable and reliable drinking water treatment.

Organo-Functionalization: An Effective Method in Enhancing the Separation and Antifouling Performance of Thin-Film Nanocomposite Membranes by Improving the Uniform Dispersion of Palygorskite Nanoparticles

Recently, palygorskite (Pal) has become a promising new membrane additive in flux enhancement and fouling reduction, which is an environmentally friendly nanoclay material under the 2:1 layer composition with 1D tubular structure. However, the aggregation of Pal due to the intermolecular forces is still an obstacle to be solved in improving membrane performance. Herein, Pal nanoparticles were chemically modified by KH550 to weaken the aggregation and improve the dispersibility, and then incorporated into the organic phase to prepare thin-film nanocomposite (TFN) membranes. The results showed that the organo-functionalization could effectively improve the membrane hydrophilicity and dispersion of Pal nanoparticles in the polyamide layer, which contributed to the enhanced water flux (from 25 to 38 L/m2·h), unchanged salt rejection (98.0%) and better antifouling capacity (91% flux recovery rate), which suggested that the organo-functionalization of nanoparticles was an efficient method in further enhancing membrane performance.

Photocatalytic Nanofiber Membranes for the Degradation of Micropollutants and Their Antimicrobial Activity: Recent Advances and Future Prospects

This review paper systematically evaluates current progress on the development and performance of photocatalytic nanofiber membranes often used in the removal of micropollutants from water systems. It is demonstrated that nanofiber membranes serve as excellent support materials for photocatalytic nanoparticles, leading to nanofiber membranes with enhanced optical properties, as well as improved recovery, recyclability, and reusability. The tremendous performance of photocatalytic membranes is attributed to the photogenerated reactive oxygen species such as hydroxyl radicals, singlet oxygen, and superoxide anion radicals introduced by catalytic nanoparticles such as TiO₂ and ZnO upon light irradiation. Hydroxyl radicals are the most reactive species responsible for most of the photodegradation processes of these unwanted pollutants. The review also demonstrates that self-cleaning and antimicrobial nanofiber membranes are useful in the removal of microbial species in water. These unique materials are also applicable in other fields such as wound dressing since the membrane allows for oxygen flow in wounds to heal while antimicrobial agents protect wounds against infections. It is demonstrated that antimicrobial activities against bacteria and photocatalytic degradation of micropollutants significantly reduce membrane fouling. Therefore, the review demonstrates that electrospun photocatalytic nanofiber membranes with antimicrobial activity form efficient cost-effective multifunctional composite materials for the removal of unwanted species in water and for use in various other applications such as filtration, adsorption and electrocatalysis.

Enhanced performance of porous forward osmosis (FO) membrane in the treatment of oily wastewater containing HPAM by the incorporation of palygorskite

Since the emergence of forward osmosis (FO), low energy requirements, low fouling propensity and high-water recovery have made it one of the most promising water purification technologies. However, there have been few reports focusing on the treatment of polymer flooding produced water (PFPW) using FO technology up to now. In the present work, porous FO membranes with/without palygorskite (Pal) nanoparticles were utilized as the separation membrane to evaluate the potential of a porous FO membrane in the treatment of oily wastewater containing HPAM and the effect of Pal nanoparticles on the FO performance was investigated. When the loading concentration of Pal in the membrane was 0.75 wt%, the water flux could reach 37.67 L m-2 h-1 by using 4 g L-1 poly(sodium-p-styrenesulfonate) (PSS) as draw solution under a cross-flow rate of 18.5 cm s-1, which was much higher than that for pure polysulfone (PS) membranes. Besides, the comparison between ultrafiltration (UF) and FO performance in treating HPAM solution indicated that FO possessed better antifouling capacity, since less decline and higher recovery of water flux were observed during the FO process. Furthermore, recycling the draw solution gave an almost unchanged water flux, which suggested the feasibility of draw solute regeneration in the FO process. This work broadens the application field of porous FO technology and may pave a new way in the treatment of PFPW.

Modifying thin film composite membrane with zeolitic imidazolate framework-8@polydopamine for enhanced antifouling property

Biofouling and organic fouling are major obstacles for polymeric membranes during application. In this work, zeolitic imidazolate framework-8@polydopamine (ZIF-8@PDA) nanoparticles were prepared by an aqueous synthesis strategy and incorporated into the polyamide (PA) selective layer to synthesize thin film nanocomposite membrane (TFN) during interfacial polymerization. The permeability and selectivity of the composite membrane were simultaneously improved with the introduction of ZIF-8@PDA. The water permeability of the TFN membrane increased to 3.74 ± 0.19 L/(m2·h·bar), which is 43.8% higher than that of the control membrane. Besides, the rejection of TFN membrane to sodium chloride is 98.68 ± 0.13%, which shows 0.99% increment than the unmodified membrane. Moreover, organic fouling and biofouling of the TFN membrane were also alleviated thanks to the introduction of the hydrophilic ZIF-8@PDA. The short-term filtration results indicate the performance of the TFN membrane is stable during operation.

In-situ coating TiO2 surface by plant-inspired tannic acid for fabrication of thin film nanocomposite nanofiltration membranes toward enhanced separation and antibacterial performance

A major issue hindering development of thin film nanocomposite (TFN) nanofiltration (NF) membrane is the interfacial defects induced by nanomaterial aggregation in top layer. Although various nanomaterials surface modification strategies have been developed to eliminate the interfacial defects, they usually involve extra modification steps and complex post-treatments. Inspired by the substrate-independent coating ability of tannic acid (TA) and the fact that the phenolic hydroxyl groups in TA can react with acyl chloride group in trimesoyl chloride, a TA coating solution containing TiO₂ nanoparticles was used as an aqueous phase of interfacial polymerization to prepare interfacial modified TFN NF membranes in this study. Surface modification of TiO₂ nanoparticles and interfacial polymerization can be carried out in a single step without any extra pre-modification step. It was found that the TA coating on TiO₂ nanoparticles surface could decrease TiO₂ aggregations and enhance interfacial compatibility between TiO₂ and polyester matrix. The TFN NF membrane prepared at a TiO₂ loading of 0.020 wt% exhibited a pure water flux of 28.8 L m^-2 h^-1 (284% higher than that of the controlled TFC membrane), and possessed enhanced NaCl and Na₂SO₄ rejections of 57.9% and 94.6%, respectively, breaking through the trade-off between permeability and selectivity.

Palygorskite/silver nanoparticles incorporated polyamide thin film nanocomposite membranes with enhanced water permeating, antifouling and antimicrobial performance

Palygorskite (Pal) is a highly hydrophilic clay mineral with tubular structure and high aspect ratio, which facilitates the attachment of nanoparticles to their surface. It has become a promising new membrane preparation additive due to its lotus root like tubular structure, low price and environmental friendliness. Silver nanoparticles (AgNPs) have excellent antibacterial ability, and their incorporation into the membrane can significantly improve the bacteriostasis of the membrane. Herein, Pal was coated by polydopamine (PDA), which acted as both the adhesive and reducing agent for AgNPs. The incorporation of the Pal/Ag nanocomposite resulted in a thin polyamide (PA) layer with rough surface morphology, which facilitated the improvement of membrane permeability. Furthermore, the Pal's parallel tubes with a 0.37 × 0.63 nm² cross-sectional area provided nanochannels allowing fast pass through of water molecules. The as-prepared TFN-7.5Pal/Ag membrane exhibited a permeate flux of 39.9 LMH at 16 bar, which was 1.6 times as high as that of the TFC membrane, accompanied with an acceptable NaCl rejection of 98.3%. Besides, antibacterial tests demonstrated that the TFN membrane presented excellent antibacterial performance against Escherichia coli (98.0%).

Preparation of core-shell structure Fe3O4@C@MnO2 nanoparticles for efficient elimination of U(VI) and Eu(III) ions

Radionuclide contamination has become an urgent problem with the development of nuclear power plants. Herein, chemical-decorated core-shell magnetic manganese dioxide (denoted as Fe₃O₄@C@MnO₂) composites were synthesized via transforming KMnO₄ to MnO₂ on the carbon-covered magnetite (Fe₃O₄@C) microsphere surface. It was employed to remove U(VI) and Eu(III) ions from aqueous solution under various conditions. The kinetic adsorption data were well simulated by the pseudo-second-order model and adsorption isotherms were fitted well by Langmuir model. Moreover, the maximum uptake capacities were up to 77.71 mg/g for U(VI) and 51.01 mg/g for Eu(III) at pH = 5.0 and T = 298 K. Adsorption behavior was strongly related to pH values but weakly affected by ionic strength, implying that the interaction of U(VI)/Eu(III) with Fe₃O₄@C@MnO₂ was mainly dominated by inner-sphere surface complexation. XPS analysis illustrated that the interaction of Eu(III)/U(VI) with Fe₃O₄@C@MnO₂ was associated with the strong metal bonds (MnO), hydroxyl bonded on metal (Mn-OH) and carboxyl groups (-COOH) by surface complexation and zeta potential results implied that the adsorption process was governed by electrostatic attraction. This research highlighted the outstanding performance of Fe₃O₄@C@MnO₂ in eliminating Eu(III)/U(VI) ions from aqueous solutions, which was of great significance in the future application in radionuclides' pollution treatment.