Eco-friendly Fabrication Process Research Articles

Green energy harvesting to power electronic devices using portable triboelectric nanogenerator based on waste corn husk and recycled polystyrene

Green energy harvesting devices are potential sustainable power sources for self-powered sensors, electronics, and the Internet of Things. Triboelectric nanogenerators (TENGs) based on natural polymers and waste materials can harvest green energy from vibration sources to convert it into electrical energy. These nanogenerators could substitute conventional electrochemical batteries to power future smart sensors and electronic devices without contaminating our ambient. Herein, we present a novel portable triboelectric nanogenerator formed by a waste corn husk and a recycled polystyrene (PS) plate as triboelectric layers. This nanogenerator has a compact and lightweight structure developed by a low-cost and eco-friendly fabrication process. This nanogenerator can convert vibrational kinetic energy into electrical energy, achieving a power density of 670.5 mW∙m−2 with a 51.9 MΩ load resistance and operating at 14 Hz. This portable nanogenerator includes simple signal processing and it can power an array of 472 commercial blue LEDs, a digital calculator, and a stopwatch. The output voltage of this nanogenerator is stable even after 25,211 operating cycles at 14 Hz with 25 mm of separation distance between triboelectric layers. The proposed nanogenerator has potential applications to power small electronic devices and sensors using vibrational kinetic energy from the environment.

Vitamin C-Induced Enhanced Performance of PEDOT:PSS Thin Films for Eco-Friendly Transient Thermoelectrics.

Conjugated polymer-based energy-harvesting devices hold distinctive advantages in terms of low toxicity, high flexibility, and capability of large-area integration at low cost for sustainable development. An organic thermoelectric (OTE) device has been considered one of the promising energy-harvesting candidates in recent years because it can efficiently convert low-temperature waste heat into electricity over its inorganic counterparts. However, a cruel irony is that environmentally toxic solvents and acids are utilized for fabrication and performance improvement of the OTE devices, retarding the development and use of genuinely green energy-harvesting. Here, we present eco-friendly, non-toxic strategies for a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based high-performance OTE device by incorporating a nature-abundant material, vitamin C (VC), as an additive. We found that the intrinsic polar nature and reducing ability of VC induce synergy effects of microstructure alignment with PSS removal and dedoping of PEDOT, leading to simultaneous enhancement of the electrical conductivity (>400 S cm-1) and the Seebeck coefficient (>30 μV K-1) and a resultant high thermoelectric power factor of 51.8 μW m-1 K-2. In addition, inspired by the eco-friendly fabrication process, we further demonstrated a transient OTE device, which can be fully degraded with naturally occurring substances, by fabricating it on a bio-based cellulose acetate substrate. We believe that our eco-friendly strategies from fabrication to disposal of the OTE can be applied to the development of high-performance, wearable, and bio-compatible OTE devices with minimal waste and further trigger the research on genuinely green thermal energy harvesting.

Ultrafast and Eco-Friendly Fabrication Process for Robust, Repairable Superhydrophobic Metallic Surfaces with Tunable Water Adhesion.

Superhydrophobic metallic surfaces with a water contact angle greater than 150° have attracted considerable attention in both fundamental research and industrial applications due to their special properties such as antibiofouling, drag reduction, self-cleaning, anti-icing, anticorrosion, and oil-water separation. Until now, the development of superhydrophobic practical applications is mainly limited by the process complexity, long fabrication time, coating with toxic materials, and easily damaged surface structure. To reduce the fabrication time, and simplify the process for industrial applications, an eco-friendly postprocess has been developed in this research. The superhydrophobic surfaces on the laser-textured titanium, aluminum, copper, stainless steel, and nickel substrates were fabricated extremely rapidly by a simple surface modification of only a 10 min heat treatment with nontoxic silicone oil. Hydrophobic organic group absorption has been accelerated on the silicone oil heat-treated surface and has created a low-energy surface. In addition, we demonstrated the potential of using the laser areal fluence parameter, which could be an alternative to single-laser process parameters such as scanning speed, power, and step size, to fine-tune the water adhesion behavior. Therefore, a surface that integrates different water adhesion behaviors can be easily fabricated for more complex practical applications such as controlled microdroplet transportation, microfluidic systems, and certain biomedical processes. Moreover, the robustness of superhydrophobic surfaces was confirmed by abrasion tests, knife-scratch tests, chemical durability tests, and aging tests, and their repairability was evaluated for product applications in practice.

Facile hydrophilic modification of polydimethylsiloxane-based sponges for efficient oil–water separation

In this study, an eco-friendly fabrication process for the hydrophilic polydimethylsiloxane (PDMS)-based sponge was proposed with the assistance of sugar templates and poly(dimethylsiloxane-b-ethylene oxide) (PDMS-b-PEO) block copolymer additives. The effects of sugar loadings and sugar particle sizes on sponge structure and separation performance were investigated. Manipulating sugar loadings exhibited a unique control over the porosity of sponge, which further influenced the absorption capacity and oil–water separation speed. Additionally, the surface modification of PDMS sponge from hydrophobic/oleophilic to hydrophilic/underwater oleophobic was achieved by incorporating PDMS-b-PEO. Such modified sponge demonstrated an underwater oil contact angle of 154° and a stable separation efficiency greater than 99.9% in the gravity-driven cycled filtration tests. The hydrophilic PDMS-b-PEO modified sponges highlighted herein reveal a promising potential for novel separation materials with energy-efficient and cost-effective features, which are ideal for oil spill clean-up events and wastewater treatment application.

Verarbeitungstechnologien für Geopolymere: 3D-Druck und mechanische Bearbeitung

Abstract: Geopolymers continue to attract interest owing to their good mechanical properties in combination with the ecofriendly fabrication process. However, the applications of geopolymers are still restricted to a limited field, mainly as construction materials. Designing and fabricating components of complex, intricate shape for applications beyond building materials may represent a useful approach to broaden geopolymer applications. In this study, unconventional processing and finishing technologies, such as direct ink printing, drilling, and machining are investigated to demonstrate their suitability for geopolymers. Fly ash-based geopolymers incorporating a relevant amount of waste glass demonstrated suitable flow properties to be used in a direct ink printing process. Moreover, the geopolymer specimens showed high machinability: components were drilled and machined in a lathe obtaining superior surface finish, uniform dimensional accuracy, and complex shape parts. The results presented herein indicate opportunities for expanding applications of geopolymers in areas such as mechanical engineering, where components with accurate, specifically designed shapes and surface finish are needed.

Advancing Processing Technologies for Designed Geopolymers: 3D Printing and Mechanical Machining

Abstract: Geopolymers continue to attract interest owing to their good mechanical properties in combination with the ecofriendly fabrication process. However, the applications of geopolymers are still restricted to a limited field, mainly as construction materials. Designing and fabricating components of complex, intricate shape for applications beyond building materials may represent a useful approach to broaden geopolymer applications. In this study, unconventional processing and finishing technologies, such as direct ink printing, drilling, and machining are investigated to demonstrate their suitability for geopolymers. Fly ash-based geopolymers incorporating a relevant amount of waste glass demonstrated suitable flow properties to be used in a direct ink printing process. Moreover, the geopolymer specimens showed high machinability: components were drilled and machined in a lathe obtaining superior surface finish, uniform dimensional accuracy, and complex shape parts. The results presented herein indicate opportunities for expanding applications of geopolymers in areas such as mechanical engineering, where components with accurate, specifically designed shapes and surface finish are needed.

Facile synthesis of flexible mesoporous aerogel with superhydrophobicity for efficient removal of layered and emulsified oil from water

Aerogel with porous structure and ultra-light weight is a potential sorbent for solving oils or organic solvents pollution. Herein, a type of flexible mesoporous aerogel was fabricated though a simple ambient pressure drying using methyltrimethoxysilane/dodecyltrimethoxysilane (MTMS/DTMS) as precursors and distilled water as solvent. The as-synthesized aerogel exhibits superhydrophobicity with water contact angle of 163° and low density of 0.102 g/cm3. Moreover, the aerogel can selectively separate oils and water-insoluble organic solvents on and under water, and the sorption capacities can reach up to 7.98–13.4 times its own weight. More importantly, the obtained aerogel is capable of separate surfactant-free and surfactant-stabilized oil-in-water emulsions with high separation efficiency of greater than 98.4%. In addition, the aerogel is highly resistant toward corrosive aqueous solutions (acidic, alkaline, salty solutions), harsh temperature environments (−30 and 160 °C), and mechanical abrasion. Due to eco-friendly fabrication process, low cost, and outstanding oil/water separation performance, the developed aerogel have potential application in oils or organic pollutants sorption and water purification.

In situ bridging effect of Ag2O on pressureless and low-temperature sintering of micron-scale silver paste

Silver sintering joining technology provides lead-free die attachment with excellent thermal conductivity and compatibility with high-temperature (≥300 °C) applications. However, sintering affordable micron-scale silver particles requires high temperature and the assistance of high pressures, which can damage chips and increase the manufacturing cost. In this article, we achieved the low-temperature, pressureless sintering of micron-scale silver particles by employing an active Ag2O additive as a bridge among the micron-scale silver particles. The Ag2O was reduced in situ to nanoscale silver to activate the surface of the micron-scale silver particles, resulting in the rapid diffusion and densification of silver particles at low temperature. An optimized composition of Ag-10% Ag2O exhibited a bonding strength of over 40 MPa at only 180 °C without any additional pressure. The results suggest that affordable micron-scale metal particles can be sintered using a suitable activating additive under an energy-efficient and eco-friendly fabrication process.

Facile preparation of lightweight high-strength biodegradable polymer/multi-walled carbon nanotubes nanocomposite foams for electromagnetic interference shielding

Lightweight conductive polymer composites (CPCs) have been considered as the most promising alternatives to metal-based shields for electromagnetic interference (EMI) shielding application but still face non-degradation issues. We report a facile, inexpensive and green method to implement lightweight biodegradable poly (l-lactic acid) (PLLA)-multiwalled carbon nanotubes (MWCNTs) nanocomposite foams using a combinatorial technology of pressure-induced flow (PIF) processing and supercritical carbon dioxide (Sc–CO2) foaming. Such low-density (∼0.3 g/cm3), low thickness (∼2.5 mm), high compressive strength (∼54 MPa g−1 cm3)) and highly conductive (∼3.4 S m−1) PLLA-MWCNT nanocomposite foams were first reported as an EMI shielding material: it presents high performance EMI shielding with a remarkable effectiveness and a corresponding average specific EMI SE of ∼23 dB and ∼77 dB g−1 cm3, respectively, with less reflection in the measured X-band frequency region. Considering the simple, low-cost and eco-friendly fabrication process, the lightweight, high-strength and highly conductive biodegradable polymer composite foams are expected to be used as high-performance EMI shielding materials in areas such as electronics, automobiles and packaging.

Eco-Friendly Fabrication Process of AlTiC Grain Refiner

In order to fabricate an aluminum grain refiners such as AlTiB and AlTiC, environmentally damaging fluoride-containing fumes induces an expensive emission control system. Furthermore, the problems associated with boride agglomeration in AlTiB refiner and expensive fabrication cost of AlTiC refiner have created a demand for boron-free and cheaper grain refiners. In the present study, Eco-friendly (K2TiF6-less) fabrication process of fading-less AlTiC refiner was investigated by an in-situ TiC formation through an melting of cheap Al-Ti master alloy in Graphite crucible and atomization of AlTiC melts producing AlTiC powders containing carbon with 250ppm. We aimed at evaluation of fading mechanism, then prevention of the fading at relative long holding time as well as substitution of AlTiB grain refiner for eco-friendly and cheaper cost.

Forming and sintering of porous calcium-hexaaluminate ceramics with hydraulic alumina

We have developed a new eco-friendly fabrication process for porous ceramics using hydraulic alumina (HA) and water. In the present study, we fabricated porous calcium-hexaaluminate (CaAl12O19, CA6) ceramics using this new process. A boehmite gel 3-D network was formed by the hydration of HA in HA/CaCO3 mixed slurry. The HA/CaCO3 mixed slurry was hardened by the formation of this 3-D network. Even without the addition of an organic binder, green bodies containing the 3-D network demonstrated high compressive strength and retained their original shapes. Furthermore, the water acted as a fugitive material in the green bodies. Consequently, the open porosity of the CA6 ceramics could be controlled over a wide range of 42–62.7% by the addition of water (ratio of water to HA/CaCO3 mixed powder: 0.4 to 1.6 by weight) without the use of organic fugitive materials. The results of evolved gas analysis-mass spectrometry measurements showed that the emissions from the hardened green body consisted mostly of water. Consequently, the new fabrication process for porous calcium-hexaaluminate ceramics was confirmed to be eco-friendly.

Fabrication of Porous Alumina Ceramics by New Eco-Friendly Process

We have developed a new eco-friendly fabrication process for porous ceramics using hydraulic alumina (HA) and water. In the present study, we fabricated porous alumina ceramics using this new process. A boehmite gel 3-D network was formed by the hydration of HA in HA slurry. The HA slurry was hardened by the formation of this 3-D network. Even without the addition of an organic binder, green bodies containing the 3-D network demonstrated high compressive strength. Furthermore, the water acted as a fugitive material in the green bodies. Consequently, the open porosity of sintered alumina ceramics could be controlled over a wide range of 56.6-69.1% by addition of water (ratio of water to HA powder: 1.0 to 2.0 by weight) without the use of organic fugitive materials. The results of evolved gas analysis-mass spectrometry measurements showed that the emissions from the hardened green body mostly consisted of water. Consequently, the new fabrication process for porous alumina ceramics was confirmed to be eco-friendly.