A comprehensive review of recent developments in 3D printing technique for ceramic membrane fabrication for water purification

Future trends of additive manufacturing in medical applications: An overview

Additive Manufacturing (AM) has recently demonstrated significant medical progress. Due to advancements in materials and methodologies, various processes have been developed to cater to the medical sector's requirements, including bioprinting and 4D, 5D, and 6D printing. However, only a few studies have captured these emerging trends and their medical applications. Therefore, this overview presents an analysis of the advancements and achievements obtained in AM for the medical industry, focusing on the principal trends identified in the annual report of AM3DP.

3D-Printed Materials for Wastewater Treatment

The increasing levels of water pollution pose an imminent threat to human health and the environment. Current modalities of wastewater treatment necessitate expensive instrumentation and generate large amounts of waste, thus failing to provide ecofriendly and sustainable solutions for water purification. Over the years, novel additive manufacturing technology, also known as three-dimensional (3D) printing, has propelled remarkable innovation in different disciplines owing to its capability to fabricate customized geometric objects rapidly and cost-effectively with minimal byproducts and hence undoubtedly emerged as a promising alternative for wastewater treatment. Especially in membrane technology, 3D printing enables the designing of ultrathin membranes and membrane modules layer-by-layer with different morphologies, complex hierarchical structures, and a wide variety of materials otherwise unmet using conventional fabrication strategies. Extensive research has been dedicated to preparing membrane spacers with excellent surface properties, potentially improving the membrane filtration performance for water remediation. The revolutionary developments in membrane module fabrication have driven the utilization of 3D printing approaches toward manufacturing advanced membrane components, including biocarriers, sorbents, catalysts, and even whole membranes. This perspective highlights recent advances and essential outcomes in 3D printing technologies for wastewater treatment. First, different 3D printing techniques, such as material extrusion, selective laser sintering (SLS), and vat photopolymerization, emphasizing membrane fabrication, are briefly discussed. Importantly, in this Perspective, we focus on the unique 3D-printed membrane modules, namely, feed spacers, biocarriers, sorbents, and so on. The unparalleled advantages of 3D printed membrane components in surface area, geometry, and thickness and their influence on antifouling, removal efficiency, and overall membrane performance are underlined. Moreover, the salient applications of 3D printing technologies for water desalination, oil-water separation, heavy metal and organic pollutant removal, and nuclear decontamination are also outlined. This Perspective summarizes the recent works, current limitations, and future outlook of 3D-printed membrane technologies for wastewater treatment.

A Comprehensive Review of Performance of Polyacrylonitrile-Based Membranes for Forward Osmosis Water Separation and Purification Process

Polyacrylonitrile (PAN), with its unique chemical, electrical, mechanical, and thermal properties, has become a crucial acrylic polymer for the industry. This polymer has been widely used to fabricate ultrafiltration, nanofiltration, and reverse osmosis membranes for water treatment applications. However, it recently started to be used to fabricate thin-film composite (TFC) and fiber-based forward osmosis (FO) membranes at a lab scale. Phase inversion and electrospinning methods were the most utilized techniques to fabricate PAN-based FO membranes. The PAN substrate layer could function as a good support layer to create TFC and fiber membranes with excellent performance under FO process conditions by selecting the proper modification techniques. The various modification techniques used to enhance PAN-based FO performance include interfacial polymerization, layer-by-layer assembly, simple coating, and incorporating nanofillers. Thus, the fabrication and modification techniques of PAN-based porous FO membranes have been highlighted in this work. Also, the performance of these FO membranes was investigated. Finally, perspectives and potential directions for further study on PAN-based FO membranes are presented in light of the developments in this area. This review is expected to aid the scientific community in creating novel effective porous FO polymeric membranes based on PAN polymer for various water and wastewater treatment applications.

Review on vat photopolymerization additive manufacturing of bioactive ceramic bone scaffolds

Bone defects frequently occur in clinical settings due to trauma, disease, tumors, and other causes. The clinical use of autologous bones and allograft bone, however, has several limitations, such as limited sources, donor site morbidity, and immunological rejection. Nevertheless, there is newfound hope for regenerating and repairing bone defects through the development and integration of bone tissue engineering scaffold and additive manufacturing (AM) technology, also known as 3D printing. In particular, vat photopolymerization (VPP)-AM of bioactive ceramic bone scaffolds has garnered significant interest from interdisciplinary researchers in recent years. On the one hand, VPP-AM demonstrates clear advantages in printing accuracy and speed compared to other AM and non-AM technologies. On the other hand, bioactive ceramic materials exhibit superior bioactivity, biodegradability, and mechanical properties compared to metals, polymers, and bioinert ceramics, making them one of the most promising biomaterials for developing bone scaffolds. This paper reviews the research progress of VPP-AM of bioactive ceramic bone scaffolds, covering the process principles of various VPP-AM technologies, the performance requirements and preparation process of VPP ceramic slurry, the VPP process of bioactive ceramic bone scaffolds, and the research progress on different material types of VPP bioactive ceramic scaffolds. Firstly, we provide a brief introduction to the process principles and medical applications of various VPP technologies. Secondly, we explore the composition of the VPP ceramic slurry system, discussing the function of various components and their effects on printing quality. Thirdly, we delve into the performance requirements of bone scaffolds and summarize the research progress of VPP bioactive ceramic bone scaffolds of various material types including hydroxyapatite (HA), tricalcium phosphate (TCP), bioglass (BG), etc.; Finally, we discuss the challenges currently faced by VPP-AM bioactive ceramic bone scaffolds and propose possible development directions for the future.

Recent Advances in the Production of Pharmaceuticals Using Selective Laser Sintering

Selective laser sintering (SLS) is an additive manufacturing process that has shown promise in the production of medical devices, including hip cups, knee trays, dental crowns, and hearing aids. SLS-based 3D-printed dosage forms have the potential to revolutionise the production of personalised drugs. The ability to manipulate the porosity of printed materials is a particularly exciting aspect of SLS. Porous tablet formulations produced by SLS can disintegrate orally within seconds, which is challenging to achieve with traditional methods. SLS also enables the creation of amorphous solid dispersions in a single step, rather than the multi-step process required with conventional methods. This review provides an overview of 3D printing, describes the operating mechanism and necessary materials for SLS, and highlights recent advances in SLS for biomedical and pharmaceutical applications. Furthermore, an in-depth comparison and contrast of various 3D printing technologies for their effectiveness in tissue engineering applications is also presented in this review.

Development of 3D ZnO-CNT Support Structures Impregnated with Inorganic Salts

Carbon-based materials are promising candidates for enhancing thermal properties of phase change materials (PCMs) without lowering its energy storage capacity. Nowadays, researchers are trying to find a proper porous structure as PCMs support for thermal energy storage applications. In this context, the main novelty of this paper consists in using a ZnO-CNT-based nanocomposite powder, prepared by an own hydrothermal method at high pressure, to obtain porous 3D printed support structures with embedding capacity of PCMs. The morphology of 3D structures, before and after impregnation with three PCMs inorganic salts (NaNO₃, KNO₃ and NaNO₃:KNO₃ mixture (1:1 vol% saturated solution) was investigated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). For structure impregnated with nitrates mixture, SEM cross-section morphology suggest that the inorganic salts impregnation started into micropores, continuing with the covering of the 3D structure surface and epitaxial growing of micro/nanostructured crystals, which led to reducing the distance between the structural strands. The variation of melting/crystallization points and associated enthalpies of impregnated PCMs and their stability during five repeated thermal cycles were studied by differential scanning calorimetry (DSC) and simultaneous DSC-thermogravimetry (DSC-TGA). From the second heating-cooling cycle, the 3D structures impregnated with NaNO₃ and NaNO₃-KNO₃ mixture are thermally stable.

Enhancement of wastewater treatment performance using 3D printed structures: A major focus on material composition, performance, challenges, and sustainable assessment

In order to enhance the performance and sustainability of wastewater treatment technologies, researchers are showing keen interest in the development of novel materials which can overcome the drawbacks associated with conventional materials. In this context, 3D printing gained significant attention due to its capability of fabricating complex geometrics using different material compositions. The present review focuses on recent advancements of 3D printing applications in various physicochemical and biological wastewater treatment techniques. In physicochemical treatment methods, substantial research has been aimed at fabricating feed spacers and other membrane parts, photocatalytic feed spacers, catalysts, scaffolds, monoliths, and capsules. Several advantages, such as membrane fouling mitigation, enhanced degradation efficiency, and recovery and reusability potential, have been associated with the aforementioned 3D printed materials. While in biofilm-based biological treatment methods, the use of 3D printed bio-carriers has led to enhanced mass transfer efficiency and microbial activities. Moreover, the application of these bio-carriers has shown better removal efficiency of chemical oxygen demand (∼90%), total nitrogen (∼73%), ammonia nitrogen (95%), and total phosphorous (∼100%). Although the removal efficiencies were comparable with conventional carriers, 3D printed carriers led to ∼40% reduction in hydraulic retention time, which could significantly save capital and operational expenditures. This review also emphasizes the challenges and sustainability aspects of 3D printing technology and outlines future recommendations which could be vital for further research in this field.

A trial to convert a polymer FDM 3D printer to handle clay materials

The research aims to show the ability to convert the Fused Deposition Modeling 3D printer to be compatible with the clay mixture after modifying the structure, setting up Cura software, and changing the print head technology. This solution provides research teams and scientists with opportunities in several ways (manufacture patch antenna substrate, dielectric automobile sensors, and ceramic dielectric aerospace technology). Additive manufacturing allows the production of many intricate shapes with ceramics, which is difficult with a traditional method. This paper used WASP ceramic slurry as raw material for Liquid Deposition Modeling (LDM) of various samples using the Archimedes screw and air pressure dispensing technique (a two-step process). LDM is a low-cost and straightforward technology appropriate for the clay prototype scale. Different clay-built shapes have been produced with water-to-clay ratios ranging from 0.57 to 0.69. The effect of the nozzle size in printing experiment tests is demonstrated. The experiment tested the print head (extruder) mechanism, the properties of the materials suitable for the putty, and how the wet slurry material is extruded from the nozzle. The optimum air pressure and slicing configuration for efficient printing are provided. Samples were stress-tested after they were dried for 24 h at average laboratory temperature and then exposed to 1000$$^\circ $$ ∘ for 1 h.

Ti(C,N) and WC-Based Cermets: A Review of Synthesis, Properties and Applications in Additive Manufacturing

In recent years, the use of cermets has shown significant growth in the industry due to their interesting features that combine properties of metals and ceramics, and there are different possible types of cermets, depending on their composition. This review focuses on cemented tungsten carbides (WC), and tungsten carbonitrides (WCN), and it is intended to analyze the relationship between chemical composition and processing techniques of these materials, which results in their particular microstructural and mechanical properties. Moreover, the use of cermets as a printing material in additive manufacturing or 3D printing processes has recently emerged as one of the scenarios with the greatest projection, considering that they manufacture parts with greater versatility, lower manufacturing costs, lower raw material expenditure and with advanced designs. Therefore, this review compiled and analyzed scientific papers devoted to the synthesis, properties and uses of cermets of TiC and WC in additive manufacturing processes reported thus far.

The emerging role of 3D printing in water desalination

Unmatched flexibility in terms of material selection, design and scalability, along with gradually decreasing cost, has led 3D printing to gain significant attention in various water treatment and desalination applications. In desalination, 3D printing has been applied to improve the energy efficiency of existing technologies. For thermal desalination, this involves the use of 3D printed components that enhance water evaporation and energy harvesting with new materials and designs. For membrane-based desalination, 3D printing offers membranes and other module components with customized materials and geometries for better fouling resistance and productivity. This review highlights the current status, advances and challenges associated with 3D printing in both thermal and membrane-based desalination technologies. Other unique benefits offered by 3D printing for water desalination along with the associated challenges are also discussed in this review. Finally, the future prospects and research directions are highlighted related to the application of 3D printing in the water desalination industry.

Green Approaches for Sustainable Development of Liquid Separation Membrane

Water constitutes one of the basic necessities of life. Around 71% of the Earth is covered by water, however, not all of it is readily available as fresh water for daily consumption. Fresh water scarcity is a chronic issue which poses a threat to all living things on Earth. Seawater, as a natural resource abundantly available all around the world, is a potential water source to fulfil the increasing water demand. Climate-independent seawater desalination has been touted as a crucial alternative to provide fresh water. While the membrane-based desalination process continues to dominate the global desalination market, the currently employed membrane fabrication materials and processes inevitably bring adverse impacts to the environment. This review aims to elucidate and provide a comprehensive outlook of the recent efforts based on greener approaches used for desalination membrane fabrication, which paves the way towards achieving sustainable and eco-friendly processes. Membrane fabrication using green chemistry effectively minimizes the generation of hazardous compounds during membrane preparation. The future trends and recommendations which could potentially be beneficial for researchers in this field are also highlighted.

A review on spacers and membranes: Conventional or hybrid additive manufacturing?

Over the past decade, 3D printing or additive manufacturing (AM) technology has seen great advancement in many aspects such as printing resolution, speed and cost. Membranes for water treatment experienced significant breakthroughs owing to the unique benefits of additive manufacturing. In particular, 3D printing's high degree of freedom in various aspects such as material and prototype design has helped to fabricate innovative spacers and membranes. However, there were conflicting reports on the feasibility of 3D printing, especially for membranes. Some research groups stated that technology limitations today made it impossible to 3D print membranes, but others showed that it was possible by successfully fabricating prototypes. This paper will provide a critical and comprehensive discussion on 3D printing specifically for spacers and membranes. Various 3D printing techniques will be introduced, and their suitability for membrane and spacer fabrication will be discussed. It will be followed by a review of past studies associated with 3D-printed spacers and membranes. A new category of additive manufacturing in the membrane water industry will be introduced here, known as hybrid additive manufacturing, to address the controversies of 3D printing for membrane. As AM technology continues to advance, its possibilities in the water treatment is limitless. Some insightful future trends will be provided at the end of the paper.

Optimizing the Axial Resistance Profile of Submerged Hollow Fiber Membranes

Submerged hollow fiber membranes (SHFMs) are used for a wide variety of applications. Their applicability and their advantages, however, depend crucially on the prevailing hydrodynamics within single fibers. In this respect, the non-uniform distribution of transmembrane flux is a known problem related to inhomogeneous membrane fouling and disadvantages for cleaning. To address this problem, we propose an approach to homogenize transmembrane flux by varying the local membrane resistance using optimal control methods for the first time in SHFM research. Based on an established model, different scenarios are optimized, namely with different fiber lengths and inner radii. In addition, a double-end setup is explored. It is shown that the optimization goal is reached very well in all tested cases, which underlines the general validity of our strategy. Further uses and extensions of the optimization method are provided, as well as hints for the practical implementation of the suggested measures.

Review of manufacturing three-dimensional-printed membranes for water treatment

With the exacerbation of industrialization, water treatment has become a necessary step for the eradication of dyes, heavy metals, oils, pharmaceuticals, and illicit drugs. These pollutants pose an impending threat to the health of humans by causing chronic or acute poisoning. Albeit they are noxious, the presence of some metals in lower concentrations is indispensable for human health. 3D printing (additive manufacturing) (3DP) can contrive nearly any complicated geometric form in a wide array of objects among various scales by a layer-wise method of manufacturing, which is more indubitably designed than any other conventional method. 3DP could remodel the existing patterns of membrane housing and possibly trim down the power demand and chemical use in saltwater desalinating and wastewater purification plants. Membranes that are 3D printed with correctly arranged apertures and shapes enhance material transport and flow athwart the surface of the membrane and at once lessen membrane soiling. This kind of technology forges membranes of polymers, biopolymers, alloys, metals, and ceramics via computer-aided design (CAD). A polylactic acid porous super-hydrophobic membrane with pore size in the range 40-600 μm showed 99.4% oil-water separating power and 60 kL h^-1 m^-2 flux when the pore size was tuned to 250 μm via CAD-aided 3D printing technology. This review focuses on the ability of 3D-printed membranes for the efficient removal of toxic pollutants from wastewater. Graphical abstract 3D-printed membranes for water treatment.

Graphitic carbon nitride nanotubes: a new material for emerging applications

We provide a critical review of the current state of the synthesis and applications of nano- and micro-tubes of layered graphitic carbon nitride. This emerging material has a huge potential for light-harvesting applications, including light sensing, artificial photosynthesis, selective photocatalysis, hydrogen storage, light-induced motion, membrane technologies, and can become a major competitor for such established materials as carbon and titania dioxide nanotubes. Graphitic carbon nitride tubes (GCNTs) combine visible-light sensitivity, high charge carrier mobility, and exceptional chemical/photochemical stability, imparting this material with unrivaled photocatalytic activities in photosynthetic processes, such as water splitting and carbon dioxide reduction. The unique geometric GCNT structure and versatility of possible chemical modifications allow new photocatalytic applications of GCNTs to be envisaged including selective photocatalysts of multi-electron processes as well as light-induced and light-directed motion of GCNT-based microswimmers. Closely-packed arrays of aligned GCNTs show great promise as multifunctional membrane materials for the light energy conversion and storage, light-driven pumping of liquids, selective adsorption, and electrochemical applications. These emerging applications require synthetic routes to GCNTs with highly controlled morphological parameters and composition to be available. We recognize three major strategies for the GCNT synthesis including templating, supramolecular assembling of precursors, and scrolling of nano-/microsheets, and outline promising routes for further progress of these approaches in the light of the most important emerging applications of GCNTs.

A review of 3D printing techniques for environmental applications

With a wide variety of techniques and compatible materials, three-dimensional (3D) printing is becoming increasingly useful in environmental applications in air, water, and energy. Through the advantages of quick production, cost-effectiveness, customizable design, the ability to produce complex geometries, and more, 3D printing has supported improvements to air quality monitors, filters, membranes, separation devices for water treatment, microbial fuel cells, solar cells, and wind turbines. It also supports sustainable manufacturing through reduced material waste, energy use, and carbon emissions. Applications of 3D printing within four environmental disciplines are described in this article: sustainable manufacturing, air quality, water and wastewater, and alternative energy sources.

Review on Blueprint of Designing Anti-Wetting Polymeric Membrane Surfaces for Enhanced Membrane Distillation Performance

Recently, membrane distillation (MD) has emerged as a versatile technology for treating saline water and industrial wastewater. However, the long-term use of MD wets the polymeric membrane and prevents the membrane from working as a semi-permeable barrier. Currently, the concept of antiwetting interfaces has been utilized for reducing the wetting issue of MD. This review paper discusses the fundamentals and roles of surface energy and hierarchical structures on both the hydrophobic characteristics and wetting tolerance of MD membranes. Designing stable antiwetting interfaces with their basic working principle is illustrated with high scientific discussions. The capability of antiwetting surfaces in terms of their self-cleaning properties has also been demonstrated. This comprehensive review paper can be utilized as the fundamental basis for developing antiwetting surfaces to minimize fouling, as well as the wetting issue in the MD process.