Cost-Effective, High-Yield Production of Biotemplated Catalytic Tubular Micromotors as Self-Propelled Microcleaners for Water Treatment

Abstract

Micro/nano-motors (MNMs) that combine attributes of miniaturization and self-propelled swimming mobility have been explored for efficient environmental remediation in the past decades. However, their progresses in practical applications are now subject to several critical issues including a complicated fabrication process, low production yield, and high material cost. Herein, we propose a biotemplated catalytic tubular micromotor consisting of a kapok fiber (KF, abundant in nature) matrix and manganese dioxide nanoparticles (MnO2 NPs) deposited on the outer and inner walls of the KF and demonstrate its applications for rapid removal of methylene blue (MB) in real-world wastewater. The fabrication is straightforward via dipping the KF into a potassium permanganate (KMnO4) solution, featured with high yield and low cost. The distribution and amount of MnO2 can be easily controlled by varying the dipping time. The obtained motors are actuated and propelled by oxygen (O2) bubbles generated from MnO2-triggered catalytic decomposition of hydrogen peroxide (H2O2), with the highest speed at 615 μm/s (i.e., 6 body length per second). To enhance decontamination efficacy and also enable magnetic navigation/recycling, magnetite nanoparticles (Fe3O4 NPs) are adsorbed onto such motors via an electrostatic effect. Both the Fe3O4-induced Fenton reaction and hydroxyl radicals from MnO2-catalyzed H2O2 decomposition can account for the MB removal (or degradation). Results of this study, taken together, provide a cost-effective approach to achieve high-yield production of the MNMs, suggesting an automatous microcleaner able to perform practical wastewater treatment.

2D Active Nanobots Based on Soft Nanoarchitectonics Powered by an Ultralow Fuel Concentration

“…Recently, 3D micromotors have been fabricated for MB dye degradation with an efficiency of around 75 %, however, they used complex technology that required a high H 2 O 2 concentration (5-7.5 %) as fuel and detergent to facilitate propulsion. [41][42][43] In contrast, our 2D nanobots had an upper limit of 85 % MB dye removal efficiency, a 25-fold reduction in fuel concentration, and do not require any detergent, showing great potential in practical applications with ultra-low fuel concentrations.…”

Frontispiece: 2D Active Nanobots Based on Soft Nanoarchitectonics Powered by an Ultralow Fuel Concentration

“…Recently, even 3D micromotors have been fabricated for MB dye degradation with an efficiency of around 75 %, however, they used complex technology that required a high H 2 O 2 concentration (5-7.5 %) as fuel and detergent to facilitate propulsion. [41][42][43] In contrast, our 2D nanobots had an upper limit of 85 % MB dye removal efficiency, a 25-fold reduction in fuel concentration, and do not require any detergent, showing great potential in practical applications with ultra-low fuel concentrations.…”

Micromotor‐in‐Sponge Platform for Multicycle Large‐Volume Degradation of Organic Pollutants

“…[ 8–11 ] During the last decade, these micro‐ and nanodevices have been designed with the aim of eliminating a wide range of pollutants through different physical and chemical processes such as physisorption [ 12–20 ] and biological‐based capture, [ 21 ] degradation, [ 22–38 ] and cell lysis [ 39–42 ] or combination of some of them. [ 17,43,44 ] Among them, degradation processes which include catalysis, [ 23,24,30,45,46 ] photocatalysis [ 25,26,36–38 ] and enzymatic catalysis, [ 27–29 ] are the most widely used mechanisms for the removal of organic pollutants. Particularly, Fenton‐like reactions have been explored as efficient decontaminating processes of AOPs in both bubble propelled platinum [ 23,45 ] or MnO 2 [ 17,43,47 ] microtubes and cobalt ferrite microparticles (CFO), [ 48 ] demonstrating exceptional degradation rates.…”

“…Engineered micro-and nanomotors have been exploited as active microcleaners for environmental purposes, showing an outstanding degradation performance due to the associated fluid mixing, as well as an efficient contaminant sensing. [8][9][10][11] During the last decade, these micro-and nanodevices have been designed with the aim of eliminating a wide range of pollutants through different physical and chemical processes such as physisorption [12][13][14][15][16][17][18][19][20] and biological-based capture, [21] degradation, [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and cell lysis [39][40][41][42] or combination of some of them. [17,43,44] Among them, degradation processes which include catalysis, [23,24,30,45,46] photocatalysis [25,26,[36]…”

“…[8][9][10][11] During the last decade, these micro-and nanodevices have been designed with the aim of eliminating a wide range of pollutants through different physical and chemical processes such as physisorption [12][13][14][15][16][17][18][19][20] and biological-based capture, [21] degradation, [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and cell lysis [39][40][41][42] or combination of some of them. [17,43,44] Among them, degradation processes which include catalysis, [23,24,30,45,46] photocatalysis [25,26,[36][37][38] and enzymatic catalysis, …”