Carbonate Micromotors for Treatment of Construction Effluents.

Purnesh Chattopadhyay,Priyanka Sharan,Juliane Simmchen,Andrej Berndt

doi:10.3390/nano10071408

Abstract

Concrete in construction has recently gained media coverage for its negative CO2 footprint, but this is not the only problem associated with its use. Due to its chemical composition, freshly poured concrete changes the pH of water coming in contact with the surface to very alkaline values, requiring neutralization treatment before disposal. Conventional methods include the use of mineral acid or CO2 pumps, causing high costs to building companies. In this paper, we present a micromotor based remediation strategy, which consists of carbonate particles half-coated with citric acid. To achieve this half coverage spray coating is used for the first time to design Janus structures. The motors propel diffusiophoretically due to a self-generated gradient formed as the acid coverage dissolves. The locally lower pH contributes to the dissolution of the carbonate body. These motors have been employed to study neutralization of diluted concrete wash water (CWW) at microscopic scale and we achieve visualization of the pH changes occurring in the vicinity of motors using anthocyanine as pH indicator dye. The effect of citric acid-carbonates hybrid on neutralization of real CWW on macroscopic scale has also been studied. In addition, all employed chemicals are cheap, non-toxic and do not leave any solid residues behind.

Highlights

Micromotors and self-propelling particles have been suggested for various environmental remediation purposes, especially in wastewater treatment [1,2,3].Different functionalities and inherent capacities of materials have been used in this regard; mainly adsorption and disposal [4], mineralization through catalytic processes [5] and highly specific interactions have been employed
To confer asymmetry to the particles we developed a novel, clean room free, scalable strategy: the particle monolayers are spray-coated with an ethanolic citric acid (CA) solution, which quickly evaporates upon deposition and crystallizes, guaranteeing a homogeneous deposition of citric acid on the carbonate particles
We developed a cheap and easy-to-maintain proof-of-concept micromotor based solution for pH remediation of alkaline concrete wash water

Summary

Introduction

Different functionalities and inherent capacities of materials have been used in this regard; mainly adsorption and disposal [4], mineralization through catalytic processes [5] and highly specific interactions have been employed. Adsorption generally requires surface interactions, for which a high surface area is beneficial. Carbon based materials [6], especially graphene [7,8] have been used frequently and other porous materials are employed [9]. Surface modification can enable more specific interactions such as the binding of heavy metals through chelating agents [10]. Different removal strategies could be achieved through more specific interplays, as has been demonstrated for hydrophobic interactions enabling the collection of oil droplets [11,12]

Methods

Results

Conclusion