A facile method to modify polypropylene membrane by polydopamine coating via inkjet printing technique for superior performance

Experimental Study on the Chlorine-Induced Corrosion and Blister Formation of Steel Pipes Coated with Modified Polyethylene Powder

In this study, chlorine-induced corrosion and blister formation on steel pipes (SPs) coated with modified polyethylene powder (MPP) were evaluated through various tests, including chlorine exposure, wet immersion, and temperature gradient experiments. The results confirmed that the extent of corrosion and iron leaching varied with the coating type as expected. In batch leaching tests, no corrosion was observed on modified polyethylene-coated steel pipes (MPCSPs) within a chlorine concentration range of 0 mg/L to 10 mg/L; similarly, there were no significant changes in specimen weight or iron levels. In contrast, the control group with uncoated SPs exhibited significant iron leaching and corrosion, a trend consistent in sequential leaching experiments. SEM analysis after a month of chlorine exposure revealed no significant corrosion on MPCSPs, and SEM-EDX confirmed no major changes in the carbon bond structure, indicating resistance to high chlorine concentrations. Comparative analysis of wet immersion and temperature gradient tests between MPCSP and conventional epoxy-coated SP (ECSP) specimens revealed that MPCSPs did not develop blisters even after 100 days of immersion, whereas ECSPs began showing blisters as early as 50 days. In temperature gradient tests, MPCSPs showed no blisters after 100 days, while ECSPs exhibited severe internal coating layer blisters.

Recyclable Fe3O4@UiO-66-PDA core-shell nanomaterials for extensive metal ion adsorption: Batch experiments and theoretical analysis

With the ever-increasing challenge of heavy metal pollution, the imperative for developing highly efficient adsorbents has become apparent to remove metal ions from wastewater completely. In this study, we introduce a novel magnetic core-shell adsorbent, Fe3O4@UiO-66-PDA. It features a polydopamine (PDA) modified zirconium-based metal-organic framework (UiO-66) synthesized through a simple solvothermal method. The adsorbent boasts a unique core-shell architecture with a high specific surface area, abundant micropores, and remarkable thermal stability. The adsorption capabilities of six metal ions (Fe3+, Mn2+, Pb2+, Cu2+, Hg2+, and Cd2+) were systematically investigated, guided by the theory of hard and soft acids and bases. Among these, three representative metal ions (Fe3+, Pb2+, and Hg2+) were scrutinized in detail. The activated Fe3O4@UiO-66-PDA exhibited exceptional adsorption capacities for these metal ions, achieving impressive values of 97.99 mg/g, 121.42 mg/g, and 130.72 mg/g, respectively, at pH 5.0. Moreover, the adsorbent demonstrated efficient recovery from aqueous solution using an external magnet, maintaining robust adsorption efficiency (>80%) and stability even after six cycles. To delve deeper into the optimized adsorption of Hg2+, density functional theory (DFT) analysis was employed, revealing an adsorption energy of -2.61 eV for Hg2+. This notable adsorption capacity was primarily attributed to electron interactions and coordination effects. This study offers valuable insights into metal ion adsorption facilitated, by magnetic metal-organic framework (MOF) materials.

Non-covalent small molecule partnership for redox-active films: Beyond polydopamine technology

HYPOTHESIS

The possibility to use hexamethylenediamine (HMDA) to impart film forming ability to natural polymers including eumelanins and plant polyphenols endowed with biological activity and functional properties has been recently explored with the aim to broaden the potential of polydopamine (PDA)-based films overcoming their inherent limitations. 5,6-dihydroxyindole-2-carboxylic acid, its methyl ester (MeDHICA) and eumelanins thereof were shown to exhibit potent reducing activity.

EXPERIMENTS

MeDHICA and HMDA were reacted in aqueous buffer, pH 9.0 in the presence of different substrates to assess the film forming ability. The effect of different reaction parameters (pH, diamine chain length) on film formation was investigated. Voltammetric and AFM /SEM methods were applied for analysis of the film redox activity and morphology. HPLC, MALDI-MS and ¹HNMR were used for chemical characterization. The film reducing activity was evaluated in comparison with PDA by chemical assays and using UV stressed human immortalized keratinocytes (HaCat) cells model.

FINDINGS

Regular and homogeneous yellowish films were obtained with moderately hydrophobic properties. Film deposition was optimal at pH 9, and specifically induced by HMDA. The film consisted of HMDA and monomeric MeDHICA accompanied by dimers/small oligomers, but no detectable MeDHICA/HMDA covalent conjugation products. Spontaneous assembly of self-organized networks held together mainly by electrostatic interactions of MeDHICA in the anion form and HMDA as the dication is proposed as film deposition mechanism. The film displayed potent reducing properties and exerted significant protective effects from oxidative stress on HaCaT.

Biomimetic, mussel-inspired surface modification of 3D-printed biodegradable polylactic acid scaffolds with nano-hydroxyapatite for bone tissue engineering

Polylactic acid (PLA) has been widely used as filaments for material extrusion additive manufacturing (AM) to develop patient-specific scaffolds in bone tissue engineering. Hydroxyapatite (HA), a major component of natural bone, has been extensively recognized as an osteoconductive biomolecule. Here, inspired by the mussel-adhesive phenomenon, in this study, polydopamine (PDA) coating was applied to the surface of 3D printed PLA scaffolds (PLA@PDA), acting as a versatile adhesive platform for immobilizing HA nanoparticles (nHA). Comprehensive analyses were performed to understand the physicochemical properties of the 3D-printed PLA scaffold functionalized with nHA and PDA for their potent clinical application as a bone regenerative substitute. Scanning electron microscopy (SEM) and element dispersive X-ray (EDX) confirmed a successful loading of nHA particles on the surface of PLA@PDA after 3 and 7 days of coating (PLA@PDA-HA3 and PLA@PDA-HA7), while the surface micromorphology and porosity remain unchanged after surface modification. The thermogravimetric analysis (TGA) showed that 7.7 % and 12.3% mass ratio of nHA were loaded on the PLA scaffold surface, respectively. The wettability test indicated that the hydrophilicity of nHA-coated scaffolds was greatly enhanced, while the mechanical properties remained uncompromised. The 3D laser scanning confocal microscope (3DLS) images revealed that the surface roughness was significantly increased, reaching Sa (arithmetic mean height) of 0.402 μm in PLA@PDA-HA7. Twenty-eight days of in-vitro degradation results showed that the introduction of nHA to the PLA surface enhances its degradation properties, as evidenced by the SEM images and weight loss test. Furthermore, a sustainable release of Ca²⁺ from PLA@PDA-HA3 and PLA@PDA-HA7 was recorded, during the degradation process. In contrast, the released hydroxyl group of nHA tends to neutralize the local acidic environments, which was more conducive to osteoblastic differentiation and extracellular mineralization. Taken together, this facile surface modification provides 3D printed PLA scaffolds with effective bone regenerative properties by depositing Ca²⁺ contents, improving surface hydrophilicity, and enhancing the in-vitro degradation rate.

Application of Capillary Polypropylene Membranes for Microfiltration of Oily Wastewaters: Experiments and Modeling

Oily wastewaters are considered as one of the most dangerous types of environmental pollution. In the present study, the microfiltration (MF) process of model emulsions and real oily wastewaters was investigated. For this purpose, capillary polypropylene (PP) membranes were used. The experiments were conducted under transmembrane pressure (TMP) and feed flow rate (VF) equal to 0.05 MPa and 0.5 m/s, respectively. It was found that the used membranes ensured a high-quality permeate with turbidity equal to about 0.4 NTU and oil concentration of 7–15 mg/L. As expected, a significant decrease in the MF process performance was noted. However, it is shown that the initial decline of permeate flux could be slightly increased by increasing the feed temperature from 25 °C to 50 °C. Furthermore, Hermia’s models were used to interpret the fouling phenomenon occurring in studied experiments. It was determined that cake formation was the dominant fouling mechanism during filtration of both synthetic and real feeds. Through detailed studies, we present different efficient methods of membrane cleaning. Results, so far, are very encouraging and may have an important impact on increasing the use of polypropylene MF membranes in oily wastewater treatments.

Development of a nanostructured film based on samarium (III)/polydopamine on the steel surface with superior anti-corrosion and water-repellency properties

HYPOTHESIS

The application of various hydrophobic/superhydrophobic coatings on the surface of metals has become the hot topic of the recent studies. The corrosion protection effectiveness and environmental issues are two important factors that should be taken into consideration when developing advanced surface coatings. Recently, the rare-earth elements (i.e., samarium) and biopolymers (i.e., polydopamine) have attracted much attention in the metals' corrosion control field.

EXPERIMENTS

The Sm(NO₃)₃ containing solution was sprayed to the steel (St-12) sheets. Then, the Sm-modified plates were post-modified by polydopamine biopolymers that were synthesized by the self-polymerization (using tris (hydroxymethyl) aminomethane as a buffer), and oxidant-induced (using CuSO₄ as an oxidant) approaches. The structural analysis was carried out by different techniques such as contact angle (CA) test. Moreover, the electrochemical impedance spectroscopy (EIS) and polarization tests were performed to investigate the anti-corrosion performance of various samples.

FINDINGS

The CA test results revealed that by applying the nanostructured Sm-based film, the surface of the metal becomes near superhydrophobic (CA > 140°). EIS results evidenced the significant impact of the post-treatment of the Sm-treated samples by polydopamine (PDA) nanoparticles (NPs) on its corrosion protection ability enhancement. Also, the polarization test results confirmed that all treatments could retard the corrosion of steel via a mixed-type inhibition mechanism.

Impact of MWCO and Dopamine/Polyethyleneimine Concentrations on Surface Properties and Filtration Performance of Modified Membranes

The mussel-inspired method has been investigated to modify commercial ultrafiltration membranes to induce antifouling characteristics. Such features are essential to improve the feasibility of using membrane processes in protein recovery from waste streams, wastewater treatment, and reuse. However, some issues still need to be clarified, such as the influence of membrane pore size and the polymer concentration used in modifying the solution. The aim of the present work is to study a one-step deposition of dopamine (DA) and polyethyleneimine (PEI) on ultrafiltration membrane surfaces. The effects of different membrane molecular weight cut-offs (MWCO, 20, 30, and 50 kDa) and DA/PEI concentrations on membrane performance were assessed by surface characterization (FTIR, AFM, zeta potential, contact angle, protein adsorption) and permeation of protein solution. Results indicate that larger MWCO membranes (50 kDa) are most benefited by modification using DA and PEI. Moreover, PEI is primarily responsible for improving membrane performance in protein solution filtration. The membrane modified with 0.5:4.0 mg mL^-1 (DA: PEI) presented a better performance in protein solution filtration, with only 15% of permeate flux drop after 2 h of filtration. The modified membrane can thus be potentially applied to the recovery of proteins from waste streams.

Inkjet printing assisted fabrication of polyphenol-based coating membranes for oil/water separation

While polyphenol-based coating has been regarded as a promising alternative to functionalize membrane surface, it usually suffers from problems of low-efficient procedure and low utilization rate of the polyphenolic compounds, hindering its large-scale implementations. To solve these problems, this study provided a first report on inkjet printing of polyphenols (catechol (CA) or tannic acid (TA)) and sodium periodate (SP) on a polyvinylidene fluoride (PVDF) membrane to improve membrane performance. A series of analyses showed the efficient formation of homogenous films on the PVDF membrane surface and the improvement of hydrophilicity by the inkjet printing technique. The PVDF membranes decorated with the optimized polyphenolic coating exhibited a promising oil/water separation efficiency (higher than 99%) with a high average water permeation flux of 5.2 times higher than that of the pristine membrane. Meanwhile, the modified membranes illustrated a good stability under acidic conditions (pH = 2-7). The novel method proposed in this study is facile, cost-saving and environment-friendly. The advantages of the proposed method and the modified membranes demonstrated the great significance of the proposed method in practical applications.