Removal of Carbon Nanotubes from Aqueous Solutions by Sodium Hypochlorite: Effects of Treatment Conditions.

Mei Yang,Minfang Zhang,Toshiya Okazaki

doi:10.3390/toxics9090223

Mei Yang, Minfang Zhang + Show 1 more

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https://doi.org/10.3390/toxics9090223

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Abstract

The treatment of carbon nanotubes (CNTs) containing wastewater has become an important issue with increasing industrial application due to the risk CNTs may pose to the environment and human health. However, an effective method for treating wastewater containing CNTs has not been established. Recently, we proposed a method to remove CNTs from aqueous dispersions using sodium hypochlorite (NaClO). To explore the practical applications of this method, we herein investigate the influence of different conditions, such as NaClO concentration, reaction temperature, pH value, and CNT concentration, on the CNT degradation rate. The results showed that the degradation of CNTs depends strongly on temperature and NaClO concentration: the higher the temperature and NaClO concentration, the faster the degradation rate. The optimal temperature and NaClO concentration are 50–70 °C and 2–3 wt%, respectively. Lower pH accelerated the degradation rate but induced the decomposition of NaClO. Furthermore, dispersants and other substances in the solution may also consume NaClO, thus affecting the degradation of CNTs. These findings are of significance for establishing a standard technique for CNT-containing industrial wastewater treatment, and for advancing the environmental sustainability of the CNT industry.

Highlights

Due to their unique structures and outstanding electrical, thermal, optical, and mechanical properties, carbon nanotubes (CNTs), including single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), have attracted extensive interest and demonstrated great promise in numerous application areas, such as energy storage, device modeling, sporting goods, water filters, thin-film electronics, coatings, actuators, and electromagnetic shields [1,2,3,4,5,6,7,8,9]
We found that most CNTs, including SWNTs, MWNTs, and carbon nanohorns (CNHs) could be completely degraded by NaClO solution
We focused on SWNTs (SG-CNTs) of high purity and medium diameter and explored the influence of various conditions and the protein bovine serum albumin (BSA), which is commonly used for dispersing CNTs [33]

Summary

Introduction

Due to their unique structures and outstanding electrical, thermal, optical, and mechanical properties, carbon nanotubes (CNTs), including single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), have attracted extensive interest and demonstrated great promise in numerous application areas, such as energy storage, device modeling, sporting goods, water filters, thin-film electronics, coatings, actuators, and electromagnetic shields [1,2,3,4,5,6,7,8,9]. CNTs in organic or inorganic solutions, preparing fibers and films, or achieving immobilization of separate particles. These processes can produce large amounts of wastewater containing CNTs. there are increasing concerns due to the potential risk of CNTs to the environment and human health [11,12,13,14,15]. It was reported that CNTs can bio-accumulate in aquatic organisms [16,17] and significantly inhibit their growth [18,19,20,21]. In 2014, the International Agency for Research on Cancer (IARC)

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