Polydopamine-coated poly(vinylidene fluoride) membranes with high ultraviolet resistance and antifouling properties for a photocatalytic membrane reactor

We modified poly(vinylidene fluoride) (PVDF) membranes with a polydopamine (PDA) coating for photocatalytic membrane reactor application with appropriate UV resistance and studied the effects of the PDA coating conditions (i.e., coating time and dopamine concentration) and UV irradiation time on the modified PVDF membrane properties. The PVDF membrane that was surface-coated with the appropriate dopamine solution concentration and coating time played a key role in controlling the membrane properties and in protecting the modified membrane against UV radiation. The optimization of the coating condition not only completely protected the modified membrane from free-radical attack initiated through UV irradiation but also improved the membrane hydrophilicity, antifouling properties, filtration performance, and mechanical strength of the membrane. UV irradiation of the membrane that was surface-coated with a high-concentration dopamine solution for a long coating time resulted in a higher mechanical strength than that of the membrane without the application of UV irradiation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47312.     

Structural and performance properties of UV-assisted TiO2 deposited nano-composite PVDF/SPES membranes

In this research, the surface of poly (vinylidene fluoride) (PVDF)/sulfonated polyethersulfone (SPES) blend membrane prepared via immersion precipitation was modified by depositing of TiO₂ nano-particles followed by UV irradiation to activate their photocatalytic property. The membranes were characterized by FTIR, SEM, AFM, contact angle, dead end filtration (pure water flux and BSA solution flux), antifouling analysis and antibacterial activity. The FTIR spectrum confirmed the presence of OH functional groups on the PVDF/SPES membrane structure, which was the key factor for deposition, and self-assembly of TiO₂ nanoparticles on the membrane surface. The SEM and AFM images indicated that the TiO₂ nanoparticles were deposited on the PVDF/SPES membrane. The contact angle measurements showed that the hydrophilicity of PVDF/SPES membrane was strongly improved by TiO₂ deposition and UV irradiation. The filtration results indicated that the initial flux of TiO₂ deposited PVDF/SPES membranes was lower than the initial flux of neat PVDF/SPES membrane. However, the former membranes showed lower flux decline compared to the neat PVDF/SPES membrane. The BSA rejection of modified membranes was improved. The fouling analysis demonstrated that the TiO₂ deposited PVDF/SPES membranes showed the fewer tendencies to fouling. The results of antibacterial study showed that the UV irradiated TiO₂ deposited PVDF/SPES membranes possess high antibacterial property.     

PVDF／多巴胺改性二氧化钛复合膜光阻隔性研究

制备了表面包覆聚多巴胺层的二氧化钛(TiO2@PDA)复合粒子,并采用溶液刮涂法制备了聚偏氟乙烯(PVDF)／TiO2和PVDF／TiO2@PDA复合膜。利用傅立叶变换红外光谱仪、X射线光电子能谱仪、透射电子显微镜表征了复合粒子的结构,利用紫外–可见光分光光度计、对比率仪表征了复合膜的紫外–可见光阻隔性。结果表明, PVDF／TiO2复合膜对紫外光具有优异的阻隔性,但对可见光的阻隔性(即不透明度)随TiO2含量增加而先增加后不变,PVDF／TiO2@PDA复合膜的不透明度则随TiO2@PDA含量的增加而单调增大。当薄膜厚度为20μm,TiO2体积分数为10％时,PVDF／TiO2复合膜对比率(CR)值为92.8％,小于完全不透明临界值98％,而PVDF／TiO2@PDA (多巴胺处理20 min)复合膜CR值为98.39％。一定TiO2浓度下,随着多巴胺处理TiO2时间的增大,复合膜达到完全不透明所需的薄膜厚度逐渐减小。     

Preparation of silver nanoparticle immobilized fibrillar silicate by poly(dopamine) surface functionalization

Surface modified fibrillar silicate (FS) was prepared by dopamine oxide polymerization and self‐assembly of poly(dopamine) (PDA) on the FS surface, presynthesized silver nanoparticles subsequently adhered to the PDA functionalized FS (FS‐PDA) surface by simply dipping FS‐PDA in silver nanoparticles solution, owing to the metal‐binding ability of catechol and nitrogen‐containing groups on the PDA coating on the surface of FS. The chemical composition of the modified FS surface was determined by X‐ray photoelectron spectroscopy. Surface morphological changes of the FS nanofibers were observed by transmission electron microscopy. The results indicated that the in situ spontaneous oxidative polymerization of dopamine on the FS surface and the immobilization of Ag nanoparticles on the surface of FS were successful. The FS‐PDA/Ag demonstrated a significant enhancement in antibacterial properties compared to the pristine FS by using Escherichia coli as model strain. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39859.     

Fabrication of self‐cleaning poly(vinylidene fluoride) membrane with micro/nanoscaled two‐tier roughness

Based on the “lotus effect” principle, smooth microreliefs of polyvinylidene fluoride (PVDF) membrane were prepared via thermally induced phase separation process. Hydroxyl groups were introduced into PVDF membrane by pretreatment with KOH/alcohol solution. Subsequently, these hydroxyl groups grafted with (CH₃)₂SiCl₂/CH₃SiCl₃ to form nano‐clusters, which were decorated on the microreliefs of PVDF membrane. Scanning Electronic Microscopy (SEM) and Atomic Force Microscope (AFM) analysis showed the micro‐ and nano‐scale structures, similar to lotus leaf, were successfully fabricated on the PVDF membrane surface. The water contact angle and sliding angle on the fabricated lotus‐leaf‐like PVDF membrane surface were 154 and 4°, respectively. Self‐cleaning test indicated that the lotus‐leaf‐like surface of PVDF membrane has excellent superhydrophobic and self‐cleaning properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Controlled grafting from poly(vinylidene fluoride) microfiltration membranes via reverse atom transfer radical polymerization and antifouling properties

A reverse atom transfer radical polymerization (RATRP) with benzoyl peroxide (BPO)/CuCl/2,2-bipyridine (Bpy) was applied onto grafting of poly(methyl methacrylate) (PMMA) and poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) from poly(vinylidene fluoride) (PVDF) microfiltration (MF) membrane surfaces, including the pore surfaces. The introduction of peroxide and hydroperoxide groups onto the PVDF membranes was achieved by ultraviolet (UV) irradiation in nitrogen, followed by air exposure. RATRP from UV pretreated hydrophobic PVDF membranes was then performed for attaching well-defined homopolymer. The chemical composition of the modified PVDF membrane surfaces was characterized by attenuated total reflectance (ATR) FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF and the PMMA grafted PVDF membranes were measured using micro-image analysis and process software. With increase of graft concentration, the pore size of the modified membranes decreased and became uniform. Kinetic studies of homogeneous (in toluene solution) system revealed a linear increase in molecular weight with the reaction time and narrow molecular weight distribution, indicating that the chain growth from the membrane surface was a “controlled” or “living” grafting process. The introduction of the well-defined PMMA on the PVDF membrane gave rise to hydrophilicity. Protein adsorption and protein solution permeation experiments revealed that the UV pretreated hydrophobic PVDF membrane subjected to surface-initiated RATRP of methyl methacrylate (MMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) exhibited good antifouling property.     

Improving bonding strength between a hydrophilic coating layer and poly(ethylene terephthalate) braid for preparing mechanically stable braid‐reinforced hollow fiber membranes

A braid‐reinforced hollow fiber membrane with mechanically stable coating layer was prepared by coating a blended polymer dope solution on an alkaline‐treated poly(ethylene terephthalate) (PET) braid. The alkaline treatment was carried out to endow the PET braid surface with more polar groups and better hydrophilicity. The results showed that the bonding strength between the hydrophilic coating layer and modified PET braid was about two times as great as that between the coating layer and original PET braid, while the pure water permeability (PWP) of the membrane remained unchanged when the PET braid was simply treated in 3 wt % potassium hydroxide (KOH) solution at 90 °C for 1 h or 1 wt % KOH solution for 6 h. The proposed modification approach proved to be a facile, low‐cost, and effective method to improve bonding strength between the coating layer and the braid, while other properties, such as PWP and morphology of the coating layer, of the braid‐reinforced hollow fiber membranes were not altered, indicating promising potential in membrane engineering. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46104     

Mixed Matrix PVDF/Graphene and Composite‐Skin PVDF/Graphene Oxide Membranes Applied in Membrane Distillation

This work elucidates the influence of graphene (G) and graphene oxide (GO) content on the desalination performance and scaling characteristics of G/polyvinylidene fluoride (G/PVDF) mixed matrix and GO/PVDF composite‐skin membranes, applied in a direct contact membrane distillation process (DCMD). Inclusion of high quality, nonoxidized, monolayered graphene sheets as polymer membrane filler, and application of a novel GO/water‐bath coagulation method for the preparation of the GO/PVDF composite films, took place. Water permeability and desalination tests via DCMD, revealed that the optimal G content was 0.87 wt%. At such concentration the water vapor flux of the G/PVDF membrane was 1.7 times that of the nonmodified reference, while the salt rejection efficiency was significantly improved (99.8%) as compared to the neat PVDF. Similarly the GO/PVDF surface‐modified membrane, prepared using a GO dispersion with low concentration (0.5 g/L), exhibited twofold higher water vapor permeate flux as compared to the neat PVDF, but however, its salt rejection efficiency was moderate (80%), probably due to pore wetting during DCMD. The relatively low scaling tendency observed for both G and GO modified membranes is primarily attributed to their smoother surface texture as compared to neat PVDF, while scaling is caused by the deposition of calcite crystals, identified by XRPD analysis. POLYM. ENG. SCI., 59:E262–E278, 2019. © 2018 Society of Plastics Engineers     

聚多巴胺改性静电纺EVOH–SO_3Li薄膜的热力性能

由静电纺丝技术制备的EVOH–SO_3Li纳米纤维薄膜的力学性能不高,为了改善薄膜的力学性能,采用多巴胺对EVOH–SO_3Li纳米纤维膜进行改性。通过宏观形貌观察、扫描电子显微镜、傅立叶变换红外光谱分析这三种测试方法相结合,表明多巴胺粘附在纳米纤维上,并在纤维膜上进行自聚形成聚多巴胺(PDA)。热失重分析结果表明,热失重为10%时PDA改性后的隔膜较未改性的EVOH–SO_3Li纯膜提高了67℃。拉伸性能测试结果表明,浸泡浓度为0.015 mol/L时,PDA改性后的隔膜拉伸强度比纯膜提高了11.89 MPa。PDA改性后薄膜的孔隙率有所下降但吸液率提升明显,最高达到了480%。     

Preparation of polyvinylidene fluoride coating modified by well-dispersed MEA-ATO@HNTs and its photocatalytic,antistatic and thermal insulation properties

In this study, Antimony-doped tin oxide (ATO) fixed and loaded on one-dimensional halloysite nanotubes (HNTs) were fabricated using the co-precipitation method to improve photocatalytic efficiency and dispersion of ATO. After that well dispersed ATO@HNTs nanofiller (AH) modified by monoethanolamine (mAH) was also embedded in the polyvinylidene fluoride (PVDF) coating by solution blend to further broaden the application fields. The results showed the introduction of HNTs accelerates electron transfer and promotes the decomposition of rhodamine B (Rh B). More significantly, with the effect of the well-dispersed mAH nanofillers, PVDF coating containing 15% mAH degraded more than 90% of Rh B under ultraviolet (UV) irradiation for 2 h, which was 1.2 times higher than that of PVDF coating. In addition, the PVDF/mAH-15% coating exhibits excellent antistatic stability under the harsh conditions of photoaging and thermal aging. Moreover, by comparing temperature differences, the thermal insulation performance of PVDF/mAH-15 coating with 70.24% visible light transmittance is significantly improved by reducing heat conduction and radiation at the same time.     

Preparation of superhydrophobic nanocomposite fiber membranes by electrospinning poly(vinylidene fluoride)/silane coupling agent modified SiO2 nanoparticles

Superhydrophobic nanocomposite fiber membranes were prepared by blend electrospinning of poly(vinylidene fluoride) (PVDF) mixed with silane coupling agent modified SiO₂ nanoparticles. The nanoparticles were prepared by the sol–gel method, and the average particle diameter was measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The effects of the type of silane coupling agent, such as n‐octyltriethoxysilane, vinyltrimethoxysilane (A‐171), and vinyltriethoxysilane (A‐151), and the mass ratio of the modified silica particles and PVDF on the surface wettability of the composite fiber membrane were investigated. The results indicated that the incorporation of silane coupling agent modified silica particles into the PVDF membrane increased the roughness of the surface and formed micro/nano dual‐scale structure compared to the pristine PVDF membrane, which was responsible for the superhydrophobicity and self‐cleaning property of the nanocomposite fiber membranes. The value of water contact angle (CA) increased with the increase of the content of modified SiO₂ nanoparticles in the nanocomposite membrane, ranging from 149.8° to 160.1° as the mass ratio of modified 170 nm SiO₂ with PVDF matrix increased from 0.5:1 to 5:1, indicating the membrane possesses a superhydrophobic surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44501.     

Improved separation performance of polyamide based reverse osmosis membrane incorporated with poly(dopamine) coated carbon nanotubes

A series of polyamide thin-film nanocomposite (PA TFN) membranes have been fabricated by incorporating hydrophilic poly(dopamine) (PDA) coated carbon nanotubes (CNTs@PDA) into the PA selective layer via interfacial polymerization. The effects of PDA coating thickness on surface characteristics and separation performances of membranes are studied in detail. The PDA coating makes the surface of PA TFN membrane more hydrophilic, smoother and less electronegative. The desalination performance is obviously influenced by the coating thickness of PDA and the loading concentration of PDA@CNTs. The water fluxes of PDA@CNTs incorporated PA TFN membranes have been improved without sacrificing NaCl rejections. When the loading concentration is 0.0010%, the maximum water flux is 48.1 L m⁻² h increasing by 45% compared with that of pristine PA membrane. Meanwhile, the NaCl rejection is up to 99.8%. The CNTs@PDA incorporated PA TFN membranes exhibit better anti-fouling property and separation performance durability. This work proves that CNTs@PDA has great potential application in PA TFN membranes.     

对位芳纶纤维的多巴胺仿生修饰及硅烷偶联剂二次功能化

研究采用多巴胺仿生修饰和硅烷偶联剂二次功能化的新方法对对位芳纶纤维进行表面改性。多巴胺首先氧化自聚,形成聚多巴胺包覆在纤维表面,以提供功能化平台。二次功能化硅烷偶联剂单体接枝到纤维表面的聚多巴胺层,在纤维表面引入有助于提高粘合性能的表面官能团。整个表面改性过程简单,无毒和可控。表面改性后的对位芳纶纤维/橡胶复合材料的H抽出力提高了69%,高温老化后粘合力保持率也显著提升。     

Facile surface modification of PVDF microfiltration membrane by strong physical adsorption of amphiphilic copolymers

To endow the surface of poly(vinylidene fluoride) (PVDF) microfiltration (MF) membranes with hydrophilicity and antifouling property, physical adsorption of amphiphilic random copolymers of poly(ethylene glycol) methacrylate (PEGMA) and poly(methyl methacrylate) (PMMA) (P(PEGMA‐r‐MMA)) onto the PVDF membrane was performed. Scanning electron microscopy (SEM) images showed that the adsorption process had no influence on the membrane structure. Operation parameters including adsorption time, polymer concentration, and composition were explored in detail through X‐ray photoelectron spectroscopy (XPS), static water contact angle (CA), and water flux measurements. The results demonstrated that P(PEGMA‐r‐MMA) copolymers adsorbed successfully onto the membrane surface, and hydrophilicity of the PVDF MF membrane was greatly enhanced. The antifouling performance and adsorption stability were also characterized, respectively. It was notable that PVDF MF membranes modified by facile physical adsorption of P(PEGMA₅₈‐r‐MMA₃₃) even showed higher water flux and better antifouling property than the commercial hydrophilic PVDF MF membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3112–3121, 2013     

Synthesis of carbon quantum dots to fabricate ultraviolet-shielding poly(vinylidene fluoride) films

The paper presents a simple and effective approach to fabricating a poly(vinylidene fluoride) (PVDF) film with excellent ultraviolet (UV) shielding performance. Carbon quantum dots (CQDs) with a highly UV absorbing property were made via a hydrothermal reaction and were then added to a poly(vinyl alcohol) (PVA) solution. The PVDF membrane pretreated with an alkaline solution was immersed in the prepared CQD/PVA solution to coat a UV-shielding layer on the film surface. Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry, X-ray diffraction, transmission electron microscopy, and UV–visible spectrophotometry were applied to study the structure, morphology, and optical performance of the CQD particles. The stability and UV-shielding performance of the obtained PVDF-OH@CQDs/PVA composite film were further investigated. The results showed that the CQD particles with diameter of 18 nm could be well dispersed in solution. Additionally, the CQDs had fairly high UV absorbance, and the PVDF-OH@CQDs/PVA composite film could shield the UV light completely. The method described in this paper is a promising one for fabricating UV-shielding composite films. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47555.     

X‐ray scattering experiments on sputtered titanium dioxide coatings onto PVDF polymers for self‐cleaning applications

The performance of active polymer substrates used in sensor and actuator or tactile display applications can be hindered by the inevitable soiling of their surface. A possible approach to overcome this problem is to deposit a self‐cleaning coating onto the polymer surface, taking care that the layer underneath withholds its intrinsic properties. In this work, titanium dioxide, TiO₂, was naturally chosen for coating material due to its inherent photocatalytic properties. Thus, TiO₂ thin films were deposited by reactive magnetron sputtering on poly(vinilydene fluoride) ‐ (PVDF) substrates, in its α‐ (nonelectroactive) and β‐ (electroactive) phases. Wide angle x‐ray scattering (WAXS) experiments in a synchrotron were performed to monitor the crystalline structure of the polymer substrates upon thin film deposition and also to assess the crystalline structure of the TiO₂ coating at different temperatures. In the WAXS patterns of the coated α‐PVDF, the TiO₂ polymorph anatase phase can be distinguished. At the same time, no explicit diffraction peaks for anatase were detected in the coated β‐PVDF. Fourier transform infrared spectroscopy evidenced that the chemical structure of PVDF is unaffected by the coating deposition process. These structural results have been correlated with the photocatalytic properties of the TiO₂ coatings. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Hydrophilic modification of poly(vinylidene fluoride) membrane with poly(vinyl pyrrolidone) via a cross‐linking reaction

A highly hydrophilic hollow fiber poly(vinylidene fluoride) (PVDF) membrane [PVDF‐cl‐poly(vinyl pyrrolidone) (PVP) membrane] was prepared by a cross‐linking reaction with the hydrophilic PVP, which was immobilized firmly on the outer surface and cross‐section of the PVDF hollow fiber membrane via a simple immersion process. The cross‐linking between PVDF and PVP was firstly verified via nuclear magnetic resonance measurement on PVP solution after cross‐linking. The hydrophilic stability of the modified PVDF membrane was evaluated by measuring the pure water flux after different times of immersion and drying. The anti‐fouling properties were estimated by cyclic filtration of protein solution. When the cross‐linking time was as long as 6 hr and the PVP content reached 5 wt %, the pure water flux (J_v) was constant as ～ 600 L m^?2 hr^?1. The hydrophilicity of the PVDF‐cl‐PVP membrane was significantly enhanced and exhibited a good stability. The PVDF‐cl‐PVP membrane showed an excellent anti‐protein‐fouling performance during the cyclic filtration of bovine serum albumin solution. Therefore, a highly hydrophilic and anti‐protein‐fouling PVDF hollow fiber membrane with a long‐term stability can be prepared by a simple and economical cross‐linking process with PVP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

紫外接枝丙烯酸对PVDF膜表面改性的研究

以二苯甲酮为光引发剂,通过紫外辐照将亲水性单体丙烯酸接枝于聚偏氟乙烯(PVDF)膜的表面。考察了光引发剂浓度和辐照时间对接枝率的影响,并利用衰减全反射光谱和扫描电子显微镜对接枝后PVDF膜表面的化学组成和微观形貌进行了表征。结果表明:随着光引发剂浓度的增大,丙烯酸的接枝率先增大后减小。通过纯水接触角和吸水率研究了接枝后的PVDF膜的亲水性,发现接枝后的PVDF膜的亲水性得到明显改善。     

碳纳米管分散强化PVDF复合薄膜导热性能探究

采用多巴胺（DA）和3?氨基丙基?三甲氧基硅烷（APTMS）对碳纳米管（CNTs）进行DA辅助共修饰,并用溶剂浇铸法制备具有优异热性能和力学性能的聚偏氟乙烯（PVDF）复合薄膜;采用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、差示扫描量热仪（DSC）、X射线光电子能谱仪（XPS）、热常数分析仪和电子单纱强力仪等对材料的微观形貌、结晶度、导热性能和力学性能进行了表征。结果表明,经DA和APTMS共修饰后的PDA?CNTs?NH₂具有良好的分散性能;PDA?CNTs?NH₂的加入,有利于改善PVDF复合薄膜的热稳定性;与纯PVDF薄膜和PVDF/CNTs复合薄膜相比,PVDF/PDA?CNTs?NH₂复合薄膜的导热性能和力学性能显著增强,在8 %（质量分数,下同） PDA?CNTs?NH₂的填料负载下,其热导率达到0.337 9 W/（m·K）,是纯PVDF薄膜的1.78倍,其拉伸强度为52.67 MPa,是纯PVDF复合薄膜的1.36倍。     

High permeability poly(vinylidene fluoride) ultrafiltration membrane doped with polydopamine modified TiO2 nanoparticles

In order to improve the water permeability of poly(vinylidene fluoride) (PVDF) ultrafiltration (UF) membranes with low molecular weight cut-off (MWCO), polydopamine (PDA) was employed in the membrane preparation process. Owing to its merits of material-independent adhesion, PDA was coated on inorganic particles or added in coagulation bath to tailor the final membrane structure and property. The introduction of PDA broke through the permeability/selectivity trade-off of the PVDF membrane. By adding the PDA coated titanium dioxide (PDA/TiO₂) nanoparticles, water flux increased by 287% while MWCO kept similar with the pristine PVDF membrane. Thermodynamics and Kinetics of the PVDF/additives/non-solvent were analyzed and shown that nanoparticles reduced the thermodynamic stability and increased the phase separation speed, and the speed can be adjusted using different nanoparticles. Additionally, X-ray diffraction (XRD) test indicated that PVDF crystalline form changed from α phase to β phase after adding different nanoparticles. Permeability/selectivity trade-off was broken through by DA addition in coagulation bath. Compared with the original PVDF membrane, when the DA concentration of the coagulation bath was 2.0 g·L⁻¹, water flux increased by 312%, and MWCO of the PVDF membrane ranged in 10,000 to 20,000 Da as well as contact angle decreased from 81.4° to 45°.