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Powder‐based piezo‐catalysis, as an effective approach to degrade wastewater and produce hydrogen from water splitting, has been widely used in the field of energy conservation and pollution reduction. However, these hard‐to‐recycle powders pose a challenge of secondary pollution in the environment. As a result, this paper provides an alternative strategy based on the manufacture of porous ceramics as a green chemistry approach to replace ferroelectric powders currently used in traditional piezo‐catalysis. The piezo‐catalytic properties of Ba0.75Sr0.25TiO3 (BST) ceramics prepared using freeze casting and direct ink writing techniques are investigated in detail. The positive effect of introducing micro‐ and macro‐pores is explored and discovered, where a BST ceramic with hierarchical pore channels is prepared by a combination of direct ink writing and freeze casting and exhibts the highest first‐order kinetic rate constant per mass of catalysts, k, of up to 2.91 min−1 kg−1 compared to bulk BST ceramics. This study therefore provides the first report for the benefits of hierarchical porous ferroelectric ceramics used in water splitting, with an average H2 production rate reaching 848.88 nmol g−1 h−1. [ABSTRACT FROM AUTHOR]

In this study, aligned porous lead zirconate titanate ( PZT) ceramics with high pyroelectric figures-of-merit were successfully manufactured by freeze casting using water-based suspensions. The introduction of aligned pores was demonstrated to have a strong influence on the resultant porous ceramics, in terms of mechanical, dielectric, and pyroelectric properties. As the level of porosity was increased, the relative permittivity decreased, whereas the Curie temperature and dielectric loss increased. The aligned porous structure exhibited improvement in the compressive strength ranging from 19 to 35 MPa, leading to easier handling, better processability and wider applications for such type of porous material. Both types of pyroelectric harvesting figures-of-merit ( FE and F′E) of the PZT ceramics with a porosity level of 25-45 vol% increased in all porous ceramics, for example, from 11.41 to 12.43 pJ/m3/K2 and 1.94 to 6.57 pm3/J, respectively, at 25°C, which were shown to be higher than the dense PZT counterpart. [ABSTRACT FROM AUTHOR]

Ubiquitous noise pollution has been associated with significant negative impacts on human health. However, current porous sound‐absorbing materials encounter considerable obstacles such as thick density, narrow absorbing band, and limited function. Here, a facile‐producing method for lightweight and efficiently sound‐absorbing aerogels made from bacterial cellulose (BC) and poly(vinyl alcohol) (PVA) is presented. The fabricated anisotropic aerogels with directional pores exhibit a minimum density as low as 11.3 mg cm−3. Meanwhile, the lamellar aerogels with low areal density (20.89 mg cm−2) exhibit remarkable noise attenuation performance with the noise reduction coefficient of 0.51.Furthermore, the BC‐PVA‐Ba0.85Ca0.15Zr0.9Ti0.1O3 (BCZT) aerogels show enhanced sound absorption performance, and these aerogels are self‐powered sensors to monitor vehicle collisions and human gestures. The algorithm yields high accuracy in human gesture recognition (100%) based on the deep‐learning model. These aerogels offer an encouraging application prospect in the automobile field to realize car weight reduction and vehicle's intelligent control system. [ABSTRACT FROM AUTHOR]

Porous Al2O3–ZrO2 composites with homogeneous and long-range ordered channels were produced by an ice template method. An increase of the initial solids loading from 40 to 70wt.% caused the final porosity to decrease from 74% to 35%, while the compressive strength increased from 15 to 81MPa. The sample obtained from the 80wt.% suspension was not porous, and a critical velocity model is employed to explain this phenomenon. [Copyright &y& Elsevier]

Piezoelectric energy harvesting has attracted significant attention in recent years due to their high-power density and potential applications for self-powered sensor networks. In comparison to dense piezoelectric ceramics, porous piezoelectric ceramics exhibit superiority due to an enhancement of piezoelectric energy harvesting figure of merit. This paper provides a detailed examination of the effect of pore morphology on the piezoelectric energy harvesting performance of porous barium calcium zirconate titanate 0.5Ba(Zr 0.2 Ti 0.8)O 3 -0.5(Ba 0.7 Ca 0.3)TiO 3 (BCZT) ceramics. Three different pore morphologies of spherical, elliptical, and aligned lamellar pores were created via the burnt-out polymer spheres method and freeze casting. The relative permittivity decreased with increasing porosity volume fraction for all porous BCZT ceramics. Both experimental and simulation results demonstrate that porous BCZT ceramics with aligned lamellar pores exhibit a higher remanent polarization. The longitudinal d 33 piezoelectric charge coefficient decreased with increasing porosity volume fraction for the porous ceramics with three different pore morphologies; however, the rate of decrease in d 33 with porosity is slower for aligned lamellar pores, leading to the highest piezoelectric energy harvesting figure of merit. Moreover, the peak power density of porous BCZT ceramics with aligned lamellar pores is shown to reach up to 38 μW cm-2 when used as an energy harvester, which is significantly higher than that of porous BCZT ceramics with spherical or elliptical pores. This work is beneficial for the design and manufacture of porous ferroelectric materials in devices for piezoelectric energy harvesting applications. [ABSTRACT FROM AUTHOR]

In this article ice templating is used to fabricate novel TiO 2 /chitosan/reduced graphene oxide (rGO) composites with a highly aligned macroporous structure for photocatalytic applications. The structure of the composites was readily tailored using the composite composition, for example the lamellar pore width decreased from 50–45 to 5–10 μm, while the lamellar thickness increased from 2–3 to 20–25 μm, with an increase of the TiO 2 content from 45 to 77 vol%. Lamellar pore channels between the layers exhibited a more uniform distribution when the rGO content was 1.0 wt%. The increase in viscosity of the composites with high TiO 2 contents led to the formation of smaller ice crystals and smaller lamellar pore sizes to enable the production of composite structures with improved mechanical strength. The TiO 2 /chitosan/rGO composites exhibited excellent photocatalytic degradation of methyl orange and the photocatalytic efficiency was optimized by control of the active material content and microstructure. The hybrid composites with 1.0 wt% rGO showed a degradation percentage of 97%, which makes these novel TiO 2 /chitosan/rGO freeze cast structures attractive materials as high performance and high strength substrates for photocatalytic degradation applications. [ABSTRACT FROM AUTHOR]

Microspheres with hollow and/or porous structures have been widely used in various applications. A new method of spraying and freezing emulsions was developed to prepare hollow HA (hydroxyapatite) microspheres with interconnected pores by using PVA (polyvinyl alcohol) as emulsifiers and binders. The relationships between viscosity and shear time or rates were tested and the dispersing stability of oil in water (O/W) emulsions was characterized with comparison to suspensions without the addition of oil phase. The effects of solid loadings of HA and the volume ratio between oil and water on the morphologies of microspheres were investigated. Hollow HA microspheres with particle diameter of ~ 20 μm and pore size of ~ 0.6 μm were successfully obtained by spray freezing method. Besides, drying and sintering processes were crucial to the formation of hollow and porous structures, respectively. The gentamicin loading and releasing of HA porous microspheres with different hollow volumes were tested. [ABSTRACT FROM AUTHOR]

TiO 2 films with ordered porous structure were prepared by freezing. By simply freezing wet TiO 2 film on a cold copper plate, ice crystals could grow from bottom of film. Removing such ice crystals then led to ordered, micro-sized pores in the films. With assistance of scanning electron microscopy and N 2 adsorption–desorption isotherms, micro-structural properties of the films were studied. Coarsening behavior of ice crystals was analyzed based on evolvement of the micro-structure. It was found that, both larger film thickness and longer freezing time were beneficial for the formation of ordered porous structure, which was caused by enhanced ice crystals growth. The films were then used to fabricate photoanode of dye sensitized solar cells, of which the photo-to-electric power conversion efficiency was evaluated. It was observed that, solar cell made of ordered porous TiO 2 film came out with 13% larger photo-current density comparing to that made of conventional doctor blading method, which is due to the enhanced light scattering by the ordered porous structure. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) microspheres with high porosities were successfully obtained using an improved ice-templated spray drying (ITSD) technique for drug delivery applications. Pore structures and pore sizes of microspheres have great impact on drug loading and release kinetics. Therefore, solvent types, polyvinyl alcohol (PVA) contents and solid loadings of suspensions were adjusted to control the pore structures and pore sizes. Microspheres with interconnected pore networks and aligned pore structures were obtained using camphene-based and tert-butyl alcohol (TBA)-based suspensions, respectively. With the increase of PVA contents in suspensions, the growth of sintering neck became more obvious and the surface of HA particles became smoother. The inner pore structures of microspheres transformed from uniformly distributed cellular pores to three-dimensional interconnected pore networks, with the increase of solid loadings in suspensions. Gentamicin was successfully loaded into porous HA microspheres. The drug loading percentage increased from 40.59 to 49.82% with the increase of porosity of HA microspheres. The release percentage during the initial 18 h increased from 48.72 to 65.68% with the transformation of pore structures from independent cellular pores (main diameter ~ 3 μm) to three-dimensional interconnected pore networks (main diameter > 3 μm). [ABSTRACT FROM AUTHOR]

Abstract: It was proposed that the piezoelectric effect played an important physiological role in bone growth, remodelling and fracture healing. An aligned porous piezoelectric composite scaffold was fabricated by freeze casting hydroxyapatite/barium titanate (HA/BT) suspensions. The highest compressive strength and lowest porosity of 14.5MPa and 57.4% with the best parallelism of the pore channels were achieved in the HA10/BT90 composite. HA30/BT70 and HA10/BT90 composites exhibited piezoelectric coefficient d 33 of 1.2 and 2.8pC/N, respectively, both of which were higher than the piezoelectric coefficient of natural bone. Increase of the solid loading of the suspension and solidification velocity led to the improvement of piezoelectric coefficient d 33. Meanwhile, double-templates resulted in the coexistence of lamellar pores and aligned macro-pores, exhibiting the ability to produce an oriented long-range ordered architecture. The manipulation flexibility of this method indicated the potential for customized needs in the application of bone substitute. An MTT assay indicated that the obtained scaffolds had no cytotoxic effects on L929 cells. [Copyright &y& Elsevier]

Abstract: A novel ice-templated spray drying technique was developed for producing uniform Al2O3 microspheres with controlled pore structures. Surface morphologies of microspheres demonstrated a higher sphericity degree with the increase of solid loading from 1 to 10vol%. The pore structure of microspheres transformed from randomly distributed pores to aligned macropores, when the spray-height more than doubled using 10vol% solid loading suspension. The thickness of the aligned pore structure was also influenced by the liquid nitrogen volume in the apparatus. [Copyright &y& Elsevier]

Abstract: Porous CaSiO3 bioceramics with open and unidirectional macro-channels of pore size more than 200μm are of particular interest for biomedical applications. An ice/fiber-templated method was employed for the fabrication of CaSiO3 bioceramics with interconnected lamellar pores and macro-channels of pore size more than 200μm. The pores formed by ice crystals transformed from cellular to lamellar, while the pores formed by fibers were aligned macro-channels, which were also in alignment with the lamellar pores. Keeping the initial slurry concentration constant and increasing the packing density of fibers, the volume fraction of macro-channels and open porosity increased, and the compressive strength decreased. Maintaining the packing density of fibers and increasing the initial slurry concentration, the pore sizes of lamellar pores and open porosity decreased, and the compressive strength increased. The results indicated that it was possible to manufacture porous CaSiO3 bioceramics with the macro-channels of 250–350μm, lamellae spacing of 50–100μm, open porosity of 71.12–83.94% and compressive strength of 0.87–3.59MPa, indicating the suitability for tissue engineering. [Copyright &y& Elsevier]

Abstract: Freeze casting of aqueous suspension was investigated as a method for fabricating hydroxyapatite (HA) porous ceramics with lamellar structures. The rheological properties of HA suspensions employed in the ice-templated process were investigated systematically. Well aligned lamellar pores and dense ceramic walls were obtained successfully in HA porous ceramics with the porosity of 68–81% and compressive strength of 0.9–2.4MPa. The results exhibited a strong correlation between the rheological properties of the employed suspensions and the morphology and mechanical properties of ice-templated porous HA ceramics, in terms of lamellar pore characteristics, porosities and compressive strengths. The ability to produce aligned pores and achieve the manipulation of porous HA microstructures by controlling the rheological parameters were demonstrated, revealing the potential of the ice-templated method for the fabrication of HA scaffolds in biomedical applications. [Copyright &y& Elsevier]