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3D-printed flexible thermoplastic polyurethane membrane for ultrafast oil/ water separation
用於超快速油/水分離的 3D 列印柔性熱塑性聚氨酯膜

Junpeng Zhang a , e C a , e C ^(a,e)C{ }^{\mathrm{a}, \mathrm{e}} \mathfrak{C}, Yingying Li b b ^(b){ }^{\mathrm{b}}, Bin He a , b , e He a , b , e He^(a,b,e)\mathrm{He}^{\mathrm{a}, \mathrm{b}, \mathrm{e}}, Tao Zhang c c ^(c){ }^{\mathrm{c}}, Bingqian Yang d d ^(d){ }^{\mathrm{d}}, Wenzheng Yu d Yu d Yu^(d)\mathrm{Yu}^{\mathrm{d}}, Ligang Hu a,b,d,f,* © a,b,d,f,*  ©  ^("a,b,d,f,* ")^("© "){ }^{\text {a,b,d,f,* }}{ }^{\text {© }}©, Guibin Jiang a,b,d a,b,d  ^("a,b,d "){ }^{\text {a,b,d }}
張 a , e C a , e C ^(a,e)C{ }^{\mathrm{a}, \mathrm{e}} \mathfrak{C} 俊鵬 ， 李 b b ^(b){ }^{\mathrm{b}} 瑩瑩 ， 張斌 He a , b , e He a , b , e He^(a,b,e)\mathrm{He}^{\mathrm{a}, \mathrm{b}, \mathrm{e}} c c ^(c){ }^{\mathrm{c}} ， 張濤 ， 楊 d d ^(d){ }^{\mathrm{d}} 秉倩 ， 鄭文正 Yu d Yu d Yu^(d)\mathrm{Yu}^{\mathrm{d}} ， 胡立剛 a,b,d,f,* © a,b,d,f,*  ©  ^("a,b,d,f,* ")^("© "){ }^{\text {a,b,d,f,* }}{ }^{\text {© }}© ， 江 a,b,d a,b,d  ^("a,b,d "){ }^{\text {a,b,d }} 桂斌 a a  ^("a "){ }^{\text {a }} State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (RCEES, CAS), Beijing 100085, China
a a  ^("a "){ }^{\text {a }} 中國科學院生態環境研究中心， 環境化學與生態毒理學國家重點實驗室， 中國科學院 北京市 100085 b b ^(b){ }^{\mathrm{b}} School of Environment, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China
b b ^(b){ }^{\mathrm{b}} 中國科學院大學 杭州高等研究院 環境學院， 中國 杭州 310024 c c  ^("c "){ }^{\text {c }} National Engineering Research Center of Industrial Wastewater Detoxication and Resource Recovery, RCEES, CAS, Beijing 100085, China
c c  ^("c "){ }^{\text {c }} 中國科學院工業廢水脫毒與資源化國家工程研究中心100085， 北京 d d  ^("d "){ }^{\text {d }} Key Laboratory of Drinking Water Science and Technology, RCEES, CAS, Beijing 100085, China
d d  ^("d "){ }^{\text {d }} 中國科學院 RCEES 飲用水科學與技術重點實驗室， 北京 100085 e e  ^("e "){ }^{\text {e }} College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
e e  ^("e "){ }^{\text {e }} 中國科學院大學 資源與環境學院， 北京 100049 f f ^(f){ }^{\mathrm{f}} Institute of Environment and Health, Jianghan University, Wuhan 430056, China
f f ^(f){ }^{\mathrm{f}} 江漢大學環境與健康研究院，中國 武漢 430056

ARTICLE INFO  文章資訊

Keywords:  關鍵字：

3D printing  3D 列印
Selective laser sintering
選擇性激光燒結
TPU  熱塑性聚氨酯
Oil/water separation  油/水分離

Abstract  抽象

The purification of oily wastewater from diverse industries emerges as a critical solution to alleviate the existing freshwater crisis. Advanced oil-water separation techniques, including membrane separation, have garnered significant attention for their high efficiency, low energy consumption, and ease of maintenance. Notably, the integration of superhydrophobic surfaces in membrane fabrication has shown promise in enhancing separation performance. However, conventional methods often fail to ensure long-term wear resistance and scalability, necessitating innovative strategies for membrane preparation. In this context, 3D printing technology, particularly selective laser sintering (SLS), presents a novel approach for the tailored production of hydrophobic membranes. By leveraging the inherent properties of thermoplastic polyurethane (TPU) and thermoplastic elastomers (TPE), untreated polymer powders can be directly sintered into intricate porous structures with micro-nano rough surfaces, exhibiting superior oil-water separation capabilities. The fabricated 3D-printed membranes demonstrate exceptional hydrophobicity and oleophilicity, coupled with robust chemical, environmental, and mechanical properties and high separation efficiency ( > 99.3 % > 99.3 % > 99.3%>99.3 \% ) at an impressive separation flux of 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 xx10^(5)L*m^(-2)*h^(-1)3.23 \times 10^{5} \mathrm{~L} \cdot \mathrm{~m}^{-2} \cdot \mathrm{~h}^{-1} under gravity-driven conditions. Furthermore, the eco-friendly nature and scalability of this approach hold promise for large-scale implementation, signaling a significant step towards sustainable environmental development.
淨化來自不同行業的含油廢水已成為緩解現有淡水危機的關鍵解決方案。先進的油水分離技術，包括膜分離，因其高效率、低能耗和易於維護而受到廣泛關注。值得注意的是，超疏水表面在膜製造中的整合在提高分離性能方面顯示出前景。然而，傳統方法往往無法確保長期的耐磨性和可擴充性，因此需要創新的膜製備策略。在此背景下，3D 列印技術，特別是選擇性激光燒結 （SLS），為定製生產疏水膜提供了一種新方法。通過利用熱塑性聚氨酯 （TPU） 和熱塑性彈性體 （TPE） 的固有特性，未經處理的可再分散乳膠粉可以直接燒結成具有微納米粗糙表面的複雜多孔結構，表現出卓越的油水分離能力。製造的 3D 列印膜表現出卓越的疏水性和親油性，以及強大的化學、環境和機械性能以及高分離效率 （ > 99.3 % > 99.3 % > 99.3%>99.3 \% ），在重力驅動條件下具有令人印象深刻的分離通量 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 xx10^(5)L*m^(-2)*h^(-1)3.23 \times 10^{5} \mathrm{~L} \cdot \mathrm{~m}^{-2} \cdot \mathrm{~h}^{-1} 。此外，這種方法的環保性質和可擴展性有望大規模實施，標誌著朝著可持續環境發展邁出了重要一步。

1. Introduction  1. 引言

The increasing global population growth and environmental pollution have led to a critical freshwater resource crisis, posing a significant threat to the sustainable development of human society. The latest data from the World Resources Institute highlights that 25 countries are under extreme pressure regarding freshwater resources, impacting around 4 billion people globally [1]. Hence, the purification of oily wastewater from industries like petrochemicals, textiles, food, and transportation into clean freshwater is imperative to alleviate the ongoing freshwater crisis [2]. Currently, researchers have developed various advanced oil-water separation technologies and devices [2,3],
全球人口增長和環境污染加劇，引發了嚴重的淡水資源危機，對人類社會的可持續發展構成了重大威脅。世界資源研究所的最新數據強調，25 個國家在淡水資源方面面臨巨大壓力，影響了全球約40億人[1]。因此，將石化、紡織、食品和運輸等行業的含油廢水凈化成清潔的淡水對於緩解持續的淡水危機至關重要 [2]。目前，研究人員已經開發了各種先進的油水分離技術和設備[2,3]。
including membrane separation, gravity separation, and chemical coagulation, to address the demand for treating oily wastewater. Among these methods, membrane separation stands out for its simplicity, high efficiency, low energy consumption, and ease of maintenance, making it a preferred choice for oil-water separation [4].
包括膜分離、重力分離和化學混凝，以滿足處理含油廢水的需求。在這些方法中，膜分離以其簡單、高效、低能耗和易於維護等特點，使其成為油水分離的首選 [4]。
In recent years, constructing materials with special wetting properties, such as superhydrophobic/superoleophilic, superhydrophilic/ superoleophobic surfaces, has become a key factor in preparing efficient oil-water separation membranes [5]. The (super)hydrophobic surfaces based on low surface energy and rough structures have demonstrated great potential in oil-water separation applications. However, traditional membrane fabrication methods, which yield relatively smooth
近年來，具有特殊潤濕性能的建築材料，如超疏水/超親油、超親水/超疏油表面，已成為製備高效油水分離膜的關鍵因素[5]。基於低表面能和粗糙結構的（超）疏水表面在油水分離應用中顯示出巨大的潛力。然而，傳統的膜製造方法，其產量相對平穩
surfaces, may adversely affect the surface roughness of membranes [6]. Therefore, diverse surface modification strategies, such as sol-gel processing [7-9], chemical vapor deposition [10-12], self-assembly techniques [13-15] and various coating methods [16,17], have been explored to create hydrophobic surfaces. These methods aim to enhance the efficiency and permeation flux of oil-water separation by manipulating surface properties like free energy and roughness to achieve (super)hydrophobicity. However, many existing strategies lack durability against abrasion and are not suitable for complex threedimensional structures, leading to a decline in surface hydrophobicity with repeated usage. Consequently, there is an urgent need to develop novel, wear-resistant, and scalable approaches for constructing hydrophobic membranes that can meet practical application requirements.
表面，可能會對膜的表面粗糙度產生不利影響 [6]。因此，人們已經探索了多種表面改性策略，如溶膠-凝膠加工[7-9]、化學氣相沉積[10-12]、自組裝技術[13-15]和各種塗層方法[16,17]，以創造疏水表面。這些方法旨在通過縱自由能和粗糙度等表面特性來實現（超）疏水性，從而提高油水分離的效率和滲透通量。然而，許多現有策略缺乏耐磨性，不適用於複雜的三維結構，導致反覆使用時表面疏水性下降。因此，迫切需要開發新穎、耐磨且可擴展的方法來構建能夠滿足實際應用要求的疏水膜。
3D printing, with its advantages in structural customization, rapid prototyping, and small-batch production, has sparked considerable interest in membrane manufacturing [18-20]. Particularly, the advancements in selective laser sintering (SLS) 3D printing technology and materials have opened up novel prospects for the preparation of hydrophobic membranes. The precision afforded by the SLS process in controlling the microstructures and surface morphology of 3D objects, coupled with the incremental layering of powdered materials, facilitates the creation of intricate porous structures with rough surface characteristics. Additionally, a notable advantage of SLS printing over other 3D printing technologies is its capability for support-free manufacturing. This feature effectively reduces material consumption and simplifies post-processing procedures, presenting a more cost-effective and streamlined approach for developing hydrophobic devices.
3D 列印憑藉其在結構定製、快速原型製造和小批量生產方面的優勢，引發了人們對膜製造的巨大興趣 [18-20]。特別是，選擇性激光燒結 （SLS） 3D 列印技術和材料的進步為疏水膜的製備開闢了新的前景。SLS 工藝在控制 3D 物體的微觀結構和表面形態方面提供的精度，加上粉末材料的增量分層，有助於創建具有粗糙表面特性的複雜多孔結構。此外，SLS 列印相對於其他 3D 列印技術的一個顯著優勢是其無支撐製造能力。此功能有效地減少了材料消耗並簡化了後處理程式，為開發疏水器件提供了一種更具成本效益和簡化的方法。
Thermoplastic polyurethane (TPU) is a hydrophobic material with low surface energy, known for its excellent wear resistance and flexibility [21], making it a popular choice as the foundational support material for hydrophobic devices [22,23]. Recently, various polymer powder materials like TPU and thermoplastic elastomers (TPE) have been increasingly commercialized within the realm of 3D printing. To bolster the mechanical resilience and environmental endurance of these polymers, additives such as fillers or anti-aging agents (e.g. silicon dioxide ( SiO 2 SiO 2 SiO_(2)\mathrm{SiO}_{2} ) nanoparticles) are commonly incorporated during the formulation of 3D printing materials. This incorporation of supplementary additives brings favorable benefits to the further construction of porous structures featuring multi-scale micro/nano-rough surfaces. Therefore, it is feasible to directly manufacture (super)hydrophobic porous devices for oil-water separation through 3D printing of such materials.
熱塑性聚氨酯 （TPU） 是一種表面能低的疏水材料，以其優異的耐磨性和柔韌性而聞名 [21]，使其成為疏水器件的基礎支撐材料的熱門選擇[22,23]。最近，TPU 和熱塑性彈性體 （TPE） 等各種聚合物粉末材料在 3D 列印領域內越來越多地商業化。為了增強這些聚合物的機械彈性和環境耐受性，在 3D 列印材料的配方中通常會加入填料或抗老化劑（例如二氧化矽 （ SiO 2 SiO 2 SiO_(2)\mathrm{SiO}_{2} ） 納米顆粒）等添加劑。這種補充添加劑的加入為進一步構建具有多尺度微/納米粗糙表面的多孔結構帶來了有利的好處。因此，通過此類材料的 3D 列印直接製造用於油水分離的（超）疏水多孔器件是可行的。
This study leveraged selective laser sintering of untreated TPU and TPE powder particles to directly fabricate hydrophobic 3D-printed membranes. The membranes displayed favorable hydrophobic and oleophilic properties, along with exceptional flexibility, mechanical durability, chemical stability, and environmental resilience. Importantly, these 3D-printed membranes showcased outstanding separation efficiency ( > 99.3 % > 99.3 % > 99.3%>99.3 \% ) and high separation flux ( 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 xx10^(5)L*m^(-2)*h^(-1)3.23 \times 10^{5} \mathrm{~L} \cdot \mathrm{~m}^{-2} \cdot \mathrm{~h}^{-1} ) under gravity-driven conditions, highlighting their potential for addressing the urgent challenges of oily wastewater treatment. Additionally, the environmental impact and potential for large-scale applications were discussed, affirming the viability of these membranes in large-scale production and promoting sustainable environmental development.
這項研究利用未經處理的 TPU 和 TPE 粉末顆粒的選擇性激光燒結直接製造疏水性 3D 列印膜。這些膜表現出良好的疏水和親油性能，以及卓越的柔韌性、機械耐久性、化學穩定性和環境彈性。重要的是，這些 3D 列印膜在重力驅動條件下表現出出色的分離效率 （ > 99.3 % > 99.3 % > 99.3%>99.3 \% ） 和高分離通量 （ 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 × 10 5 L ⋅ m − 2 ⋅ h − 1 3.23 xx10^(5)L*m^(-2)*h^(-1)3.23 \times 10^{5} \mathrm{~L} \cdot \mathrm{~m}^{-2} \cdot \mathrm{~h}^{-1} ），突出了它們在解決含油廢水處理的緊迫挑戰方面的潛力。此外，還討論了環境影響和大規模應用的可能性，肯定了這些膜在大規模生產中的可行性並促進了可持續的環境發展。

2. Method and experimental section
2. 方法和實驗部分

2.1. Materials and chemicals
2.1. 材料和化學品

Thermoplastic polyurethane powders (TPU-Bright, TPU-Soft, and TPU-Grey) and thermoplastic elastomer (TPE) powder were purchased from Sinterit company (Kraków, Poland), with the product names being FLEXA Bright, FLEXA Soft, FLEXA Grey, and TPE Tight, respectively. Detailed physicochemical properties of these power materials are shown in Table S1. The n-hexane, cyclohexane, toluene, chloroform and
熱塑性聚氨酯粉末（TPU-Bright、TPU-Soft 和 TPU-Grey）和熱塑性彈性體 （TPE） 粉末購自 Sinterit 公司（波蘭克拉科夫），產品名稱分別為 FLEXA Bright、FLEXA Soft、FLEXA Grey 和 TPE Tight。這些功率材料的詳細物理化學性質如表 S1 所示。正己烷、環己烷、甲苯、氯仿和
dichloromethane, and span 80 were purchased from Sigma-Aldrich Co., Ltd. Kerosene and liquid paraffin ( 99 % 99 % 99%99 \% ) were purchased from Shanghai Macklin Biochemical Co., Ltd. Sunflower seed oil was purchased from Wu Mart supermarket in Beijing. Oil Red O, methylene blue, ethanol, sodium hydroxide ( NaOH ), sodium chloride ( NaCl ) ( NaCl ) (NaCl)(\mathrm{NaCl}), anhydrous magnesium sulfate ( MgSO 4 ) MgSO 4 (MgSO_(4))\left(\mathrm{MgSO}_{4}\right), and calcium carbonate ( CaCO 3 ) CaCO 3 (CaCO_(3))\left(\mathrm{CaCO}_{3}\right) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Hydrochloric acid ( HCl ) was purchased from Sinopharm Chemical Reagent Co., Ltd. Unless otherwise stated, all reagents used in this study were analytical grade and used as received without further purification.
二氯甲烷和跨度 80 購自 Sigma-Aldrich Co.， Ltd. 煤油和液體石蠟 （ 99 % 99 % 99%99 \% ） 購自上海麥克林生化有限公司 葵花籽油購自北京 Wu Mart 超市。油紅O、亞甲藍、乙醇、氫氧化鈉（NaOH）、氯化鈉 ( NaCl ) ( NaCl ) (NaCl)(\mathrm{NaCl}) 、無水硫酸 ( MgSO 4 ) MgSO 4 (MgSO_(4))\left(\mathrm{MgSO}_{4}\right) 鎂、碳酸 ( CaCO 3 ) CaCO 3 (CaCO_(3))\left(\mathrm{CaCO}_{3}\right) 鈣購自上海阿拉丁生化技術有限公司。鹽酸（HCl）購自國葯化學試劑有限公司。除非另有說明，本研究中使用的所有試劑均為分析級，按收到時使用，無需進一步純化。

2.2. Membrane design and 3D printing
2.2. 膜設計和 3D 列印

The 3D model of the membrane, with a diameter of 2.5 cm and a thickness of 0.8 mm , was designed utilizing SolidWorks 2021 software (Dassault Systemes, France). The remaining 3D model files (Fig. S1) are available on Thingiverse (https://www.thingiverse.com/). The 3D models were sliced into Scode. format using Sinterit Studio 2019 and printed on the Lisa printer (Sinterit, Poland) with an XY axis resolution of 50 μ m 50 μ m 50 mum50 \mu \mathrm{~m}, as illustrated in Fig. S2. The parameter settings of the different materials are shown in Table S2. The printing process involved preheating the powder bed, selective layer-by-layer sintering polymer powder with an infrared laser (Power: 5 W , wavelength: 808 nm ), and a subsequent cooling stage. After printing, any loose powder residues on the surface of 3D-printed objects were meticulously removed using a scraper and fiber brush, followed by cleaning with deionized water and air-drying overnight. This procedure intentionally avoids the use of a glass bead blasting device equipped with the printer aims to maintain surface roughness, as research has shown that a brief 30 -second sandblasting treatment can significantly reduce material surface roughness by 62-72 % [24]. Furthermore, the study investigates the impact of printing parameters on the performance of 3D-printed membranes through parameter adjustments. These parameters include the laser power ratio (ranging from 0.50 to 1.50), layer thickness (ranging from 0.075 mm to 1.50 mm ) and surface temperature offset (ranging from − 4.5 ∘ C − 4.5 ∘ C -4.5^(@)C-4.5{ }^{\circ} \mathrm{C} to 1.5 ∘ C 1.5 ∘ C 1.5^(@)C1.5{ }^{\circ} \mathrm{C} ). Following the optimization of the parameters described above, the effect of the overall membrane thickness (set from 0.25 mm to 2.00 mm ) on the membrane separation performance was also examined.
直徑為 2.5 釐米、厚度為 0.8 毫米的膜的 3D 模型是使用 SolidWorks 2021 軟體（法國達索系統）設計的。其餘的 3D 模型檔（圖 S1）可在 Thingiverse （https://www.thingiverse.com/） 上找到。3D 模型被切成 Scode。格式，並在 Lisa 印表機（Sinterit，波蘭）上列印，XY 軸解析度為 50 μ m 50 μ m 50 mum50 \mu \mathrm{~m} ，如圖 S2 所示。表 S2 顯示了不同材料的參數設置。列印過程包括預熱粉末床，使用紅外鐳射器（功率：5 W，波長：808 nm）選擇性逐層燒結聚合物粉末，以及隨後的冷卻階段。列印后，使用刮刀和纖維刷仔細去除 3D 列印物體表面的任何鬆散粉末殘留物，然後用去離子水清潔並風幹過夜。該程式有意避免使用印表機配備的玻璃珠噴砂裝置，以保持表面粗糙度，因為研究表明，短暫的 30 秒噴砂處理可以顯著降低 62-72% 的材料表面粗糙度 [24]。此外，該研究通過參數調整調查了列印參數對 3D 列印膜性能的影響。這些參數包括鐳射功率比（範圍從 0.50 到 1.50）、層厚（範圍從 0.075 毫米到 1.50 毫米）和表面溫度偏移（範圍從 − 4.5 ∘ C − 4.5 ∘ C -4.5^(@)C-4.5{ }^{\circ} \mathrm{C} 到 1.5 ∘ C 1.5 ∘ C 1.5^(@)C1.5{ }^{\circ} \mathrm{C} ）。在優化上述參數之後，還檢查了總膜厚度（設置為0.25 mm至2.00 mm）對膜分離性能的影響。

2.3. Characterization of morphology, roughness and pore size distribution
2.3. 形態、粗糙度和孔徑分佈的表徵

The surface morphology of the 3D-printed membrane was observed by a field emission scanning electron microscope (SEM, S-3000 N, Hitachi, Japan) after being sputter-coated with gold for 70 s under an acceleration voltage of 15 kV . Surface roughness and pore size distribution of the membranes were tested by 3D optical profilers (Mahr MarSurf LD130, Germany) and capillary pore size analyzer (CFP1500AE, PMI Porometer, USA), respectively. Other detailed characterizations for membranes can be found in the Supporting Text.
在 15 kV 的加速電壓下，用場發射掃描電子顯微鏡（SEM，S-3000 N，Hitachi，Japan）觀察 3D 列印膜的表面形貌。分別通過 3D 光學輪廓儀（Mahr MarSurf LD130，德國）和毛細管孔徑分析儀（CFP1500AE，PMI Porometer，美國）測試膜的表面粗糙度和孔徑分佈。膜的其他詳細表徵可以在支援文本中找到。

2.4. Porosity test  2.4. 孔隙率測試

The porosity of 3D-printed membrane was evaluated using the wetdry membrane weighing method. Specifically, the 3D-printed membrane was cleaned by immersion in ethanol solution for 2 h , then dried at 60 ∘ C 60 ∘ C 60^(@)C60^{\circ} \mathrm{C} for 24 h , and weighed to determine the mass of the dry membrane ( M 1 M 1 M_(1)M_{1} ). Subsequently, the 3D-printed membranes were fully wetted with ethanol, and immersed in deionized water for 24 h , with the deionized water being changed every 4 h , to reach saturation. The mass of the wet membrane was then measured and recorded as M 2 M 2 M_(2)M_{2}. Additionally, the thickness of each membrane was measured using an electronic digital caliper (Shanghai Shenhan Measuring Tools Co., LTD, China). The porosity of the membrane was then calculated using the following formula:
使用 Wetdry 膜稱重法評估 3D 列印膜的孔隙率。具體來說，通過將 3D 列印膜浸入乙醇溶液中 2 小時，然後乾燥 60 ∘ C 60 ∘ C 60^(@)C60^{\circ} \mathrm{C} 24 小時，並稱重以確定乾燥膜的品質 （ M 1 M 1 M_(1)M_{1} ）。隨後，將 3D 列印的膜用乙醇充分潤濕，並浸入去離子水中 24 h，每 4 h 更換一次去離子水，以達到飽和。然後測量濕膜的質量並記錄為 M 2 M 2 M_(2)M_{2} 。此外，使用電子數位卡尺（上海申韓測量工具有限公司，中國）測量每個膜的厚度。然後使用以下公式計算膜的孔隙率：
ε = ( M 2 − M 1 ) / A d ρ w × 100 % ε = M 2 − M 1 / A d ρ w × 100 % epsi=(M_(2)-M_(1))//Adrho_(w)xx100%\varepsilon=\left(M_{2}-M_{1}\right) / A d \rho_{w} \times 100 \%
in which, M 1 M 1 M_(1)M_{1} and M 2 ( g ) M 2 ( g ) M_(2)(g)M_{2}(g) represent the dry and wet mass of the 3Dprinted membrane, ε ( % ) ε ( % ) epsi(%)\varepsilon(\%) denotes the porosity, A ( cm 2 ) A cm 2 A(cm^(2))A\left(\mathrm{~cm}^{2}\right) and d ( cm ) d ( cm ) d(cm)d(\mathrm{~cm}) represent the area and thickness of the 3D-printed membranes, respectively, and ρ w ρ w rho_(w)\rho_{w} is the density of water ( 1 g ⋅ cm − 3 ) 1 g ⋅ cm − 3 (1(g)*cm^(-3))\left(1 \mathrm{~g} \cdot \mathrm{~cm}^{-3}\right).
其中， M 1 M 1 M_(1)M_{1} 和 M 2 ( g ) M 2 ( g ) M_(2)(g)M_{2}(g) 表示 3D 列印膜的幹質量和濕品質， ε ( % ) ε ( % ) epsi(%)\varepsilon(\%) 表示孔隙率， A ( cm 2 ) A cm 2 A(cm^(2))A\left(\mathrm{~cm}^{2}\right) 分別 d ( cm ) d ( cm ) d(cm)d(\mathrm{~cm}) 表示 3D 列印膜的面積和厚度， ρ w ρ w rho_(w)\rho_{w} 是水 ( 1 g ⋅ cm − 3 ) 1 g ⋅ cm − 3 (1(g)*cm^(-3))\left(1 \mathrm{~g} \cdot \mathrm{~cm}^{-3}\right) 的密度。

2.5. Contact angle measurement
2.5. 接觸角測量

The contact angles of 3D-printed membranes were measured using the OCA15EC contact angle measurement instrument (Dataphysics, Germany) in air and oil environments to assess their hydrophobic, oleophilic, and underoil water-repellent properties. For hydrophobicity assessment, a precise volume of 3 μ L 3 μ L 3muL3 \mu \mathrm{~L} water droplets was carefully applied to the membrane surface with a micro syringe, with the average contact angle determined at three different positions. The underoil water contact angle test involved using n-hexane as the oil solution, following the same testing protocol as previously described.
使用 OCA15EC 接觸角測量儀器（Dataphysics，德國）在空氣和油環境中測量 3D 列印膜的接觸角，以評估其疏水、親油和油下防水性能。為了進行疏水性評估，用微型注射器小心地將精確體積的水 3 μ L 3 μ L 3muL3 \mu \mathrm{~L} 滴施加到膜表面，並在三個不同的位置確定平均接觸角。油下水接觸角測試涉及使用正己烷作為油溶液，遵循與前面描述的相同的測試方案。

2.6. Calculation of surface tension
2.6. 表面張力的計算

The behavior of a liquid on a smooth solid surface is described by the Young equation (Equation 2), which considers the combined influence of the surface tension of the liquid ( γ l v ) γ l v (gamma_(lv))\left(\gamma_{l v}\right) and the solid ( γ s v ) γ s v (gamma_(sv))\left(\gamma_{s v}\right), and the interfacial tension between the solid and the liquid ( γ s l ) γ s l (gamma_(sl))\left(\gamma_{s l}\right).
液體在光滑固體表面上的行為由Young方程（方程 2）描述，該方程考慮了液體 ( γ l v ) γ l v (gamma_(lv))\left(\gamma_{l v}\right) 和固體 ( γ s v ) γ s v (gamma_(sv))\left(\gamma_{s v}\right) 的表面張力以及固體和液體 ( γ s l ) γ s l (gamma_(sl))\left(\gamma_{s l}\right) 之間的介面張力的綜合影響。
γ l v cos ⁡ θ = γ s v − γ s l γ l v cos ⁡ θ = γ s v − γ s l gamma_(lv)cos theta=gamma_(sv)-gamma_(sl)\gamma_{l v} \cos \theta=\gamma_{s v}-\gamma_{s l}
where θ θ theta\theta represents the contact angle. However, due to the presence of surface roughness on solid surfaces, adjustments were proposed by Wu et al. as follows:
其中 θ θ theta\theta 表示接觸角。然而，由於固體表面存在表面粗糙度，Wu 等人提出了如下調整建議：
γ s v = γ s v d + γ s v p γ s v = γ s v d + γ s v p gamma_(sv)=gamma_(sv)^(d)+gamma_(sv)^(p)\gamma_{s v}=\gamma_{s v}^{d}+\gamma_{s v}^{p}
γ l v ( 1 + cos ⁡ θ ) = 4 ( ( γ s v d γ l v d ) / ( γ s v d + γ l v d ) + ( γ s v p γ l v p ) / ( γ s v p + γ l v p ) ) γ l v ( 1 + cos ⁡ θ ) = 4 γ s v d γ l v d / γ s v d + γ l v d + γ s v p γ l v p / γ s v p + γ l v p gamma_(lv)(1+cos theta)=4((gamma_(sv)^(d)gamma_(lv)^(d))//(gamma_(sv)^(d)+gamma_(lv)^(d))+(gamma_(sv)^(p)gamma_(lv)^(p))//(gamma_(sv)^(p)+gamma_(lv)^(p)))\gamma_{l v}(1+\cos \theta)=4\left(\left(\gamma_{s v}^{d} \gamma_{l v}^{d}\right) /\left(\gamma_{s v}^{d}+\gamma_{l v}^{d}\right)+\left(\gamma_{s v}^{p} \gamma_{l v}^{p}\right) /\left(\gamma_{s v}^{p}+\gamma_{l v}^{p}\right)\right)
where γ s v d γ s v d gamma_(sv)^(d)\gamma_{s v}^{d} and γ s v p γ s v p gamma_(sv)^(p)\gamma_{s v}^{p} represents the dispersion component of the solid surface energy, and γ l v d γ l v d gamma_(lv)^(d)\gamma_{l v}^{d} and γ l v p γ l v p gamma_(lv)^(p)\gamma_{l v}^{p} correspond to the dispersion and polar components of the liquid surface energy respectively. In this study, the modified equation is utilized to calculate the surface tension of the 3Dprinted membrane.
其中 γ s v d γ s v d gamma_(sv)^(d)\gamma_{s v}^{d} 和 γ s v p γ s v p gamma_(sv)^(p)\gamma_{s v}^{p} 表示固體表面能的色散分量， γ l v d γ l v d gamma_(lv)^(d)\gamma_{l v}^{d} 和 γ l v p γ l v p gamma_(lv)^(p)\gamma_{l v}^{p} 分別對應於液體表面能的色散分量和極性分量。在本研究中，修正方程用於計算 3D 列印膜的表面張力。

2.7. Oil/water separation
2.7. 油/水分離

The oil-water separation performance of the 3D-printed membrane under the influence of gravity was assessed using a custom laboratory apparatus. The formula for calculating the oil-water separation flux is expressed as:
使用定製的實驗室設備評估了 3D 列印膜在重力影響下的油水分離性能。計算油水分離通量的公式表示為：
F = V / ( A × Δ t ) F = V / ( A × Δ t ) F=V//(A xx Delta t)F=V /(A \times \Delta t)
where F F FF denotes the oil permeation flux under the gravitational force ( L ⋅ m − 2 ⋅ h − 1 L ⋅ m − 2 ⋅ h − 1 L*m^(-2)*h^(-1)\mathrm{L} \cdot \mathrm{m}^{-2} \cdot \mathrm{~h}^{-1} ), with V V VV representing the volume of permeation in a specific time unit (L), A denoting the effective filtration area of the 3D-printed membrane ( m 2 ) m 2 (m^(2))\left(\mathrm{m}^{2}\right), and Δ t Δ t Delta t\Delta t indicating the filtration duration required to complete the separation process (h). Each test in this study involved filtering an approximate volume of 100 mL of the oil-water mixture.
其中 F F FF 表示重力作用下的油滲透通量 （ L ⋅ m − 2 ⋅ h − 1 L ⋅ m − 2 ⋅ h − 1 L*m^(-2)*h^(-1)\mathrm{L} \cdot \mathrm{m}^{-2} \cdot \mathrm{~h}^{-1} ）， V V VV 表示特定時間單位 （L） 的滲透體積，A 表示 3D 列印膜 ( m 2 ) m 2 (m^(2))\left(\mathrm{m}^{2}\right) 的有效過濾面積， Δ t Δ t Delta t\Delta t 表示完成分離過程所需的過濾持續時間 （h）。本研究中的每項測試都涉及過濾大約 100 mL 體積的油水混合物。
The calculation formula for the separation efficiency of the oil-water separation process is as follows:
油水分離過程分離效率的計算公式如下：
E = ( M A / M 0 ) × 100 % E = M A / M 0 × 100 % E=(M_(A)//M_(0))xx100%E=\left(M_{A} / M_{0}\right) \times 100 \%
where E E EE symbolizes the separation efficiency (%), M 0 M 0 M_(0)M_{0} stands for the mass of oil in the oil-water mixture before the separation process, and M A M A M_(A)M_{\mathrm{A}} is the mass of oil separated from the mixture.
其中 E E EE 表示分離效率 （%）， M 0 M 0 M_(0)M_{0} 代表分離過程前油水混合物中的油品質， M A M A M_(A)M_{\mathrm{A}} 是從混合物中分離的油的品質。

2.8. Wear resistance and flexibility test
2.8. 耐磨性和柔韌性測試

To evaluate the wear resistance of the 3D-printed membranes, they were securely fastened beneath a 500 g weight and continuously rubbed against 240-grit sandpaper ( 28 cm × 23 cm 28 cm × 23 cm 28cmxx23cm28 \mathrm{~cm} \times 23 \mathrm{~cm}, Eagle Brand). Additionally, tweezers were used to handle 3D-printed membranes made of different materials to assess their flexibility.
為了評估 3D 列印膜的耐磨性，它們被牢固地固定在 500 克的重量下，並與 240 粒度的砂紙（ 28 cm × 23 cm 28 cm × 23 cm 28cmxx23cm28 \mathrm{~cm} \times 23 \mathrm{~cm} 鷹牌）不斷摩擦。此外，鑷子還用於處理由不同材料製成的 3D 列印膜，以評估其柔韌性。

2.9. Mechanical/chemical/thermal/environmental stability test
2.9. 機械/化學/熱/環境穩定性測試

The mechanical durability of the 3D-printed membrane was assessed through the utilization of tools including files, scrapers, and scissors. To evaluate its chemical stability, the membranes underwent testing with water solutions at various pH levels ( pH = 1 , 3 , 5 , 7 , 9 , 11 , 13 pH = 1 , 3 , 5 , 7 , 9 , 11 , 13 pH=1,3,5,7,9,11,13\mathrm{pH}=1,3,5,7,9,11,13 ), high-salt solutions (up to 10 wt % 10 wt % 10wt%10 \mathrm{wt} \% concentrations of NaCl , MgSO 4 NaCl , MgSO 4 NaCl,MgSO_(4)\mathrm{NaCl}, \mathrm{MgSO}_{4}, and CaCO 3 CaCO 3 CaCO_(3)\mathrm{CaCO}_{3} ), as well as real environmental samples including milk, coffee, fruit juice, and wastewater. The thermal stability of the 3D-printed TPU-Bright membrane was assessed using a TGA 209F1 thermal analyzer (Netzsch, Germany). The membranes with a weight of 5 − 10 mg 5 − 10 mg 5-10mg5-10 \mathrm{mg} were heated from 30 to 800 ∘ C 800 ∘ C 800^(@)C800^{\circ} \mathrm{C} at a heating rate of 10 ∘ C min − 1 10 ∘ C min − 1 10^(@)Cmin^(-1)10^{\circ} \mathrm{C} \mathrm{min}^{-1} in a nitrogen atmosphere. Additionally, the performance of 3D-printed TPU-Bright membrane in separating oil-water mixtures at various temperatures was evaluated. The maximum test temperature was set at 60 ∘ C 60 ∘ C 60^(@)C60{ }^{\circ} \mathrm{C}, considering that the boiling point of the oil phase (n-hexane) is 69 ∘ C 69 ∘ C 69^(@)C69^{\circ} \mathrm{C}. Furthermore, the ability of the membranes to resist UV aging was determined by subjecting them to continuous exposure to a 39 W UV lamp over a 24 -hour duration.
通過使用包括銼刀、刮刀和剪刀在內的工具評估了 3D 列印膜的機械耐久性。為了評估其化學穩定性，膜用各種 pH 值 （ pH = 1 , 3 , 5 , 7 , 9 , 11 , 13 pH = 1 , 3 , 5 , 7 , 9 , 11 , 13 pH=1,3,5,7,9,11,13\mathrm{pH}=1,3,5,7,9,11,13 ）、高鹽溶液（高達 10 wt % 10 wt % 10wt%10 \mathrm{wt} \% NaCl , MgSO 4 NaCl , MgSO 4 NaCl,MgSO_(4)\mathrm{NaCl}, \mathrm{MgSO}_{4} 、 和 CaCO 3 CaCO 3 CaCO_(3)\mathrm{CaCO}_{3} 的濃度）以及真實的環境樣品（包括牛奶、咖啡、果汁和廢水）進行了測試。使用 TGA 209F1 熱分析儀（德國 Netzsch）評估 3D 列印 TPU-Bright 膜的熱穩定性。將重量為 的 5 − 10 mg 5 − 10 mg 5-10mg5-10 \mathrm{mg} 膜在氮氣氣氛 10 ∘ C min − 1 10 ∘ C min − 1 10^(@)Cmin^(-1)10^{\circ} \mathrm{C} \mathrm{min}^{-1} 中以加熱速率從 30 加熱到 800 ∘ C 800 ∘ C 800^(@)C800^{\circ} \mathrm{C} 。此外，還評估了 3D 列印 TPU-Bright 膜在不同溫度下分離油水混合物的性能。考慮到油相（正己烷）的沸點為 60 ∘ C 60 ∘ C 60^(@)C60{ }^{\circ} \mathrm{C} 69 ∘ C 69 ∘ C 69^(@)C69^{\circ} \mathrm{C} ，最高測試溫度設置為 。此外，膜抵抗紫外線老化的能力是通過將它們在 39 W 紫外線燈下持續暴露 24 小時來確定的。

3. Results and discussion
3. 結果和討論

3.1. Wettability of 3D-printed membranes
3.1. 3D 列印膜的潤濕性

The wettability of water and oil on the surface of 3D-printed membranes plays a critical role in oil-water separation. Contact angle tests show that different types of membranes exhibit notable hydrophobicity, as evidenced by water contact angles ranging from 127.1 ∘ 127.1 ∘ 127.1^(@)127.1^{\circ} to 142.5 ∘ 142.5 ∘ 142.5^(@)142.5^{\circ} (Fig. 1A). Among them, 3D-printed TPU membranes exhibit comparatively higher contact angles than that of TPE, likely attributed to their lower surface energy ( 11.71 ∼ 15.86 mN m − 1 11.71 ∼ 15.86 mN m − 1 11.71∼15.86mNm^(-1)11.71 \sim 15.86 \mathrm{mN} \mathrm{m}^{-1} ). Furthermore, the water contact angles of TPU-Bright and TPU-Grey membranes exceed 140 ∘ 140 ∘ 140^(@)140^{\circ}, possibly due to distinct variations in their size distribution (Table S1), which is considered to facilitate the creation of multi-scale rough surfaces ( S a > 29.08 μ m , S q > 36.05 μ m S a > 29.08 μ m , S q > 36.05 μ m (S_(a) > 29.08 mu(m),S_(q) > 36.05 mu(m):}\left(\mathrm{S}_{\mathrm{a}}>29.08 \mu \mathrm{~m}, \mathrm{~S}_{\mathrm{q}}>36.05 \mu \mathrm{~m}\right. and S z > 257.2 μ m S z > 257.2 μ m S_(z) > 257.2 mum\mathrm{S}_{\mathrm{z}}>257.2 \mu \mathrm{~m} ) (Fig. 1E and Fig. S3-S4). When wetted with water, the multi-scale rough surface causes an air layer to form between the water and the membrane, hindering the water from wetting the surface of membranes and resulting in a hydrophobic or even superhydrophobic state. Interestingly, these 3Dprinted membranes even exhibit superhydrophobic properties (156.4 ) ) )) under oil (Fig. 1C), underscoring their remarkable repellence towards aqueous solutions. Meanwhile, all 3D-printed membranes show excellent oleophilicity, displaying a strong affinity for oil in both air and water (Fig. S5). This is because oil can leverage the rough surface structure to enhance capillary forces between itself and the membrane, thus improving wettability on the membrane surface. Notably, oil can rapidly infiltrate into the 3D-printed membrane within 40 ms , demonstrating the membrane’s high oil throughput capacity. These results suggest that constructing micro-nano structured rough surface on TPU/ TPE materials through the SLS process proves advantageous for achieving hydrophobicity and oleophilicity, thereby establishing a solid foundation for further advancements in efficient oil-water separation.
水和油在 3D 列印膜表面的潤濕性在油水分離中起著至關重要的作用。接觸角測試表明，不同類型的膜表現出顯著的疏水性，水接觸角從 127.1 ∘ 127.1 ∘ 127.1^(@)127.1^{\circ} 到 142.5 ∘ 142.5 ∘ 142.5^(@)142.5^{\circ} 就證明瞭這一點（圖 1A）。其中，3D 列印的 TPU 膜表現出比 TPE 相對更高的接觸角，這可能是由於它們的表面能較低 （ 11.71 ∼ 15.86 mN m − 1 11.71 ∼ 15.86 mN m − 1 11.71∼15.86mNm^(-1)11.71 \sim 15.86 \mathrm{mN} \mathrm{m}^{-1} ）。此外，TPU-Bright 和 TPU-Grey 膜的水接觸角超過 140 ∘ 140 ∘ 140^(@)140^{\circ} ，可能是由於它們的尺寸分佈發生了明顯的變化（表 S1），這被認為有助於創建多尺度粗糙表面 ( S a > 29.08 μ m , S q > 36.05 μ m S a > 29.08 μ m , S q > 36.05 μ m (S_(a) > 29.08 mu(m),S_(q) > 36.05 mu(m):}\left(\mathrm{S}_{\mathrm{a}}>29.08 \mu \mathrm{~m}, \mathrm{~S}_{\mathrm{q}}>36.05 \mu \mathrm{~m}\right. 和 S z > 257.2 μ m S z > 257.2 μ m S_(z) > 257.2 mum\mathrm{S}_{\mathrm{z}}>257.2 \mu \mathrm{~m} ）（圖 1E 和圖 S3-S4）。當被水潤濕時，多尺度的粗糙表面會導致在水和膜之間形成空氣層，阻礙水潤濕膜表面，導致疏水甚至超疏水狀態。有趣的是，這些 3D 列印膜甚至表現出超疏水特性（ ) ) )) 在油下為 156.4（圖 1C），強調了它們對水溶液的顯著排斥性。同時，所有 3D 列印膜都顯示出優異的親油性，對空氣和水中的油表現出很強的親和力（圖 S5）。這是因為油可以利用粗糙的表面結構來增強自身與膜之間的毛細管力，從而提高膜表面的潤濕性。值得注意的是，油可以在 40 毫秒內迅速滲入 3D 打印膜中，證明瞭該膜的高油吞量能力。 這些結果表明，通過 SLS 工藝在 TPU/TPE 材料上構建微納米結構的粗糙表面被證明有利於實現疏水性和親油性，從而為高效油水分離的進一步發展奠定了堅實的基礎。

3.2. Morphology and porosity of 3D-printed TPU-Bright membranes with different printing parameters
3.2. 不同列印參數的 3D 列印 TPU-Bright 膜的形態和孔隙率

To achieve optimal membrane performance, a subsequent printing parameter optimization was carried out on the TPU-Bright membrane
為了實現最佳膜性能，對 TPU-Bright 膜進行了後續列印參數優化
    • Corresponding author at: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
      通訊作者：中國科學院生態環境研究中心，環境化學與生態毒理學國家重點實驗室，北京100085。
    E-mail address: lghu@rcees.ac.cn (L. Hu).
    電子郵件地址：lghu@rcees.ac.cn （L. 胡）。