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Mullite fibers possess low thermal conductivity, excellent high-temperature stability, and thermal shock resistance, making them extensively utilized in high-temperature heat-insulating components. However, the majority of current mullite fibers have solid structures, limiting the potential for further enhancement of their heat-insulating properties. Metaplexis fiber, a plant fiber with a hollow structure, effectively obstructs heat transfer, and therefore exhibits excellent heat-insulating properties. In this study, we employed metaplexis fibers as templates to fabricate mullite fibers with hollow structures. First, a precursor solution was prepared using Al(NO 3) 3 ·9H 2 O and ethyl orthosilicate as the solute and anhydrous ethanol as the solvent. The metaplexis fibers were immersed in the solution, removed, and dried to obtain precursor fibers. Finally, the precursor fibers were heated to the target temperature to obtain hollow mullite fibers. The investigation focused on the impact of preparation parameters such as sintering temperature, precursor solution concentration, and aluminum–silicon molar ratio on the morphologies, phases, pore-size distributions, and thermal conductivities of the resulting hollow mullite fibers. The results demonstrated that the prepared mullite fibers inherited the hollow structure of metaplexis fibers, with the cavity diameter in the range of 3–6 μm and porosity of 91 %. Compared to traditional solid mullite fibers, the thermal insulation performance was improved by more than 59 %. These findings highlight the significant potential of hollow ceramic fibers for the development of heat-insulating materials. Using the unique characteristics of their hollow structure, these fibers offer improved heat-insulating properties compared to their solid counterparts. [ABSTRACT FROM AUTHOR]

• A novel strategy for oil-in-water droplet coalescence was proposed on basis of microchannel-structured anodes. • The microchannel enhanced droplet polarization to weaken the electrostatic repulsion. • The microchannel improved ∙OH utilization to decompose oil-water interface film. • Residence time was 48 times shorter than that of reported flat electrodes at similar COD removal. • Excellent stability and unique renewability performance were achieved. Electrochemistry is a sustainable technology for oil-water separation. In the common flat electrode scheme, due to a few centimeters away from the anode, oil droplets have to undergo electromigration to and electrical neutralization at the anodic surface before they coalesce into large oil droplets and rise to water surface, resulting in slow demulsification and easy anode fouling. Herein, a novel strategy is proposed on basis of a TiO 2-x /Ti anode with microchannels to overcome these problems. When oil droplets with several microns in diameter flow through channels with tens of microns in diameter, the electromigration distance is shortened by three orders of magnitude, electrical neutralization is replaced by polarization coupling ·OH oxidation. The new strategy was supported by experimental results and theoretical analysis. Taking the suspension containing emulsified oil as targets, COD value dropped from initial 500 mg/L to 117 mg/L after flowing through anodic microchannels in only 58 s of running time, and the COD removal was 21 times higher than that for a plate anode. At similar COD removal, the residence time was 48 times shorter than that of reported flat electrodes. Coalescences of oil droplets in microchannels were observed by a confocal laser scanning microscopy. This new strategy opens a door for using microchannel electrodes to accelerate electrochemical coalescence of oil-in-water droplets. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel membrane-free electrochemical reactor was proposed for water softening. • OH¯ diffusion was propelled by upward bubbles motion and downward water flow. • The alkaline region was enlarged, extending to bulk solution. • Homogeneous nucleation occupied a high proportion in the hardness removal. • The softening efficiency was higher than that in reported membrane-free works. Electrochemistry is a potential method for water softening. An essential disadvantage is OH¯ ions from water electrolysis accumulate on cathode surface, inducing the generation of the insulating CaCO 3 layer and then interrupting the electrochemical reaction. In order to propel OH¯ diffusion into the bulk solution instead of aggregation at cathode, we designed an electrochemical reactor, whose electrodes were placed horizontally in the middle of the reactor, and the bubbles created by water electrolysis move upward, while the water flows downward. The visual evidence displayed that the unique reactor structure allowed OH¯ to spread to almost all the solution rapidly. Average pH value of bulk solution reached 10.6 in only 3 min. Therefore, homogeneous nucleation of CaCO 3 in bulk solution would take primary responsibility for water softening, and the softening efficiency is up to 212.9 g CaCO 3 /h/m2, higher than reported results. The reactor is easy to scale up, providing a new idea for the softening of circulating cooling water. [Display omitted] [ABSTRACT FROM AUTHOR]

Electrocatalytic nitrate reduction has been regarded as an efficient alternative route for ammonia production. Developing efficient, economical and environment-friendly cathodes is a significant concern for the practical applications of this method. Herein, we report a charcoal electrode fabricated by carbonizing natural wood for efficient nitrate reduction. It displays high overpotential for hydrogen evolution, moderate sp3 C structure and oxygen-containing surface groups. Benefiting from these features, the charcoal cathode exhibits high nitrate removal rate (91.2%), outstanding selectivity (98.5%) and fast production rate (0.570 mmol L−1 h−1 cm−2) for ammonium. Both removal rate and selectivity are superior to other carbon materials and comparable to metal-containing cathodes. These results exhibit the possibility of using charcoal as cathodes for denitrification and ammonia recovery from wastewater. • Charcoal cathodes were fabricated via carbonizing natural wood. • Efficiency of nitrate reduction was up to 91.2%. • Selectivity of ammonium production was 96.0%. • Good performance was ascribed to abundant sp3 C and surface C–O groups. [ABSTRACT FROM AUTHOR]

A novel electrochemical sensor basing on an indium tin oxide (ITO) glass electrode modified by hydroxyapatite (HAp) film was fabricated by electrodeposited method for simultaneous detection of Pb 2+ , Cu 2+ and Hg 2+ using differential pulse voltammetry (DPV). Various experimental parameters such as supporting electrolyte and pH were optimized. Under the optimal conditions, the electrode needs no accumulate time. The electrode showed linear correlation in the ranges of 1 × 10 −7 to 1 × 10 −6  M and 3 × 10 −6 to 1 × 10 −5  M for Pb 2+ , 1 × 10 −7 to 1 × 10 −6  M and 1 × 10 −6 to 1 × 10 −5  M for Cu 2+ , and 1 × 10 −7 to 1 × 10 −5  M for Hg 2+ . The limits of detection (S/N = 3) were 1 × 10 −12 , 1 × 10 −12 , 8 × 10 −8  M for Pd 2+ , Cu 2+ and Hg 2+ , respectively. Meanwhile, the developed electrode showed excellent anti-interference capabilities and selectivity with other heavy metal ions and common ions. The electrode has been successfully applied to the detection of above heavy metal ions in tap water. Above all, two major detection mechanisms of developed electrode were also researched in this work. The mechanism of filling Ca deficiency due to that the radiuses of Pb 2+ and Cu 2+ are similar to Ca 2+ , so Pb 2+ and Cu 2+ can fill in the deficiency. That is why the detection limits of Pb 2+ and Cu 2+ are much lower than Hg 2+ . When Ca deficiency has been almost filled, the detection of Pb 2+ and Cu 2+ based on the mechanism of surface adsorption. Because the radius of Hg 2+ is not similar to Ca 2+ , Hg 2+ cannot fill in the deficiency. The detection of Hg 2+ mainly based on the mechanism of surface adsorption. The OH − on the surface of HAp plays a major role in the adsorption of heavy metal ions. [ABSTRACT FROM AUTHOR]