3D Printed Scaffolds for Monolithic Aerogel Photocatalysts with Complex Geometries

Metal-Organic Framework and Covalent-Organic Framework-Based Aerogels: Synthesis, Functionality, and Applications

Metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs)-based aerogels are garnering significant attention owing to their unique chemical and structural properties. These materials harmoniously combine the advantages of MOFs and COFs-such as high surface area, customizable porosity, and varied chemical functionality-with the lightweight and structured porosity characteristic of aerogels. This combination opens up new avenues for advanced applications in fields where material efficiency and enhanced functionality are critical. This review provides a comparative overview of the synthetic strategies utilized to produce pristine MOF/COF aerogels as well as MOF/COF-based hybrid aerogels, which are functionalized with molecular precursors and nanoscale materials. The versatility of these aerogels positions them as promising candidates for addressing complex challenges in environmental remediation, energy storage and conversion, sustainable water-energy technologies, and chemical separations. Furthermore, this study discusses the current challenges and future prospects related to the synthesis techniques and applications of MOF/COF aerogels.

Additive Manufacturing: A Paradigm Shift in Revolutionizing Catalysis with 3D Printed Photocatalysts and Electrocatalysts Toward Environmental Sustainability

Semiconductor-based materials utilized in photocatalysts and electrocatalysts present a sophisticated solution for efficient solar energy utilization and bias control, a field extensively explored for its potential in sustainable energy and environmental management. Recently, 3D printing has emerged as a transformative technology, offering rapid, cost-efficient, and highly customizable approaches to designing photocatalysts and electrocatalysts with precise structural control and tailored substrates. The adaptability and precision of printing facilitate seamless integration, loading, and blending of diverse photo(electro)catalytic materials during the printing process, significantly reducing material loss compared to traditional methods. Despite the evident advantages of 3D printing, a comprehensive compendium delineating its application in the realm of photocatalysis and electrocatalysis is conspicuously absent. This paper initiates by delving into the fundamental principles and mechanisms underpinning photocatalysts electrocatalysts and 3D printing. Subsequently, an exhaustive overview of the latest 3D printing techniques, underscoring their pivotal role in shaping the landscape of photocatalysts and electrocatalysts for energy and environmental applications. Furthermore, the paper examines various methodologies for seamlessly incorporating catalysts into 3D printed substrates, elucidating the consequential effects of catalyst deposition on catalytic properties. Finally, the paper thoroughly discusses the challenges that necessitate focused attention and resolution for future advancements in this domain.

Design and fabrication of self-suspending aluminum-plastic/semiconductor photocatalyst devices for solar energy conversion

The design and synthesis of self-suspending photocatalyst device with easy recyclability is important for practical application. Here, this work utilizes aluminum-plastic package waste as raw material to prepare an aluminum-plastic supported TiO2 (AP-TiO2) photocatalyst device through 3D printing design and surface deposition method. A series of characterizations were carried out to explore the structure, morphology and performance of the AP-TiO2 device. Under UV light illumination, the AP-TiO2-50 efficiently degrade 93.6% tetracycline hydrochloride (THC) after 4 hr, which increases by 8.3% compared with that of TiO2 powder suspension system with the same catalyst amount. Based on it, AP-ZnO, AP-CdS, AP-g-C3N4 and AP-Pt-TiO2 are also fabricated, and applied in photocatalytic degradation and hydrogen evolution, which all exhibit higher photoactivities than powder suspension systems. This work provides a new avenue for the fabrication of advanced recyclable photocatalyst device. Moreover, the work offers a novel sight for the high-value utilization of aluminum-plastic package waste, which has positive implications for environmental protection.

Optimization of Mass and Light Transport in Nanoparticle-Based Titania Aerogels

Aerogels composed of preformed titania nanocrystals exhibit a large surface area, open porosity, and high crystallinity, making these materials appealing for applications in gas-phase photocatalysis. Recent studies on nanoparticle-based titania aerogels have mainly focused on optimizing their composition to improve photocatalytic performance. Little attention has been paid to modification at the microstructural level to control fundamental properties such as gas permeability and light transmittance, although these features are of fundamental importance, especially for photocatalysts of macroscopic size. In this study, we systematically control the porosity and transparency of titania gels and aerogels by adjusting the particle loading and nonsolvent fraction during the gelation step. Mass transport and light transport were assessed by gas permeability and light attenuation measurements, and the results were related to the microstructure determined by gas sorption analysis and scanning electron microscopy. Mass transport through the aerogel network was found to proceed primarily via Knudsen diffusion leading to relatively low permeabilities in the range of 10-5-10-6 m2/s, despite very high porosities of 96-99%. While permeability was found to depend mainly on particle loading, the optical properties are predominantly affected by the amount of nonsolvent during gelation, allowing independent tuning of mass and light transport.

Designing Highly Photoactive Hybrid Aerogels for In-Flow Photocatalytic Contaminant Removal Using Silica-Coated Bacterial Nanocellulose Supports

This study explores the use of silica-coated bacterial nanocellulose (BC) scaffolds with bulk macroscopic yet nanometric internal pores/structures as functional supports for high surface area titania aerogel photocatalysts to design flexible, self-standing, porous, and recyclable BC@SiO₂-TiO₂ hybrid organic-inorganic aerogel membranes for effective in-flow photo-assisted removal of organic pollutants. The hybrid aerogels were prepared by sequential sol-gel deposition of the SiO₂ layer over BC, followed by coating of the resulting BC@SiO₂ membranes with a porous titania aerogel overlayer of high surface area using epoxide-driven gelation, hydrothermal crystallization, and subsequent supercritical drying. The silica interlayer between the nanocellulose biopolymer scaffold and the titania photocatalyst was found to greatly influence the structure and composition, particularly the TiO₂ loading, of the prepared hybrid aerogel membranes, allowing the development of photochemically stable aerogel materials with increased surface area/pore volume and higher photocatalytic activity. The optimized BC@SiO₂-TiO₂ hybrid aerogel showed up to 12 times faster in-flow photocatalytic removal of methylene blue dye from aqueous solution in comparison with bare BC/TiO₂ aerogels and outperformed most of the supported-titania materials reported earlier. Moreover, the developed hybrid aerogels were successfully employed to remove sertraline drug, a model emergent contaminant, from aqueous solution, thus further demonstrating their potential for water purification.

Embedded 3D Printing of Multimaterial Polymer Lattices via Graph-Based Print Path Planning

Recent advances in computational design and 3D printing enable the fabrication of polymer lattices with high strength-to-weight ratio and tailored mechanics. To date, 3D lattices composed of monolithic materials have primarily been constructed due to limitations associated with most commercial 3D printing platforms. Here, freeform fabrication of multi-material polymer lattices via embedded three-dimensional (EMB3D) printing is demonstrated. An algorithm is developed first that generates print paths for each target lattice based on graph theory. The effects of ink rheology on filamentary printing and the effects of the print path on resultant mechanical properties are then investigated. By co-printing multiple materials with different mechanical properties, a broad range of periodic and stochastic lattices with tailored mechanical responses can be realized opening new avenues for constructing architected matter.

The Importance of the Macroscopic Geometry in Gas-Phase Photocatalysis

Photocatalysis has the potential to make a major technological contribution to solving pressing environmental and energy problems. There are many strategies for improving photocatalysts, such as tuning the composition to optimize visible light absorption, charge separation, and surface chemistry, ensuring high crystallinity, and controlling particle size and shape to increase overall surface area and exploit the reactivity of individual crystal facets. These processes mainly affect the nanoscale and are therefore summarized as nanostructuring. In comparison, microstructuring is performed on a larger size scale and is mainly concerned with particle assembly and thin film preparation. Interestingly, most structuring efforts stop at this point, and there are very few examples of geometry optimization on a millimeter or even centimeter scale. However, the recent work on nanoparticle-based aerogel monoliths has shown that this size range also offers great potential for improving the photocatalytic performance of materials, especially when the macroscopic geometry of the monolith is matched to the design of the photoreactor. This review article is dedicated to this aspect and addresses some issues and open questions that arise when working with macroscopically large photocatalysts. Guidelines are provided that could help develop novel and efficient photocatalysts with a truly 3D architecture.