Microporous assembly of MnO 2 nanosheets for malachite green degradation Sandip Saha b,a , Anjali Pal a,⇑ a Department of Civil Engineering, Indian Institute of Technology, Kharagpur 721302, India b Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India article info Article history: Received 4 May 2014 Received in revised form 9 July 2014 Accepted 10 July 2014 Available online 18 July 2014 Keywords: MnO 2 nanosheet Porous soft assembly Malachite green Oxidative degradation Mineralization abstract Porous assembly of MnO 2 nanosheets has been prepared via a simple redox co-precipitation method using Mn(OAc) 2 and KMnO 4 . The material has been characterized by XRD, XPS, FESEM, TEM, FTIR, and N 2 -adsorption–desorption analyses. The as-prepared MnO 2 nanomaterial is microporous (average pore diameter: 0.8 nm; surface area: 162 m 2 /g) and poorly crystalline. The TEM and SEM images reveal the for- mation of spherical assembly of fine nanosheets. The oxidation state of manganese is determined by XPS analysis. The porous nature and the oxidizing property of the nano MnO 2 has been exploited for MG deg- radation in aqueous media under ambient condition. The effects of various parameters (such as pH, MnO 2 dose, initial MG concentration, air/O 2 , and organic acids) on MG degradation are evaluated. The mineral- ization of MG is monitored through TOC analyses. About 99% decolorization and 44% mineralization of MG (conc.: 50 mg/L) is achieved in 120 min with MnO 2 (dose: 0.5 g/L). The decolorization follows first order kinetics. During the oxidative degradation, slight leaching of Mn 2+ is observed. The reusability of the material has been shown for three consecutive cycles with good performance. Ó 2014 Published by Elsevier B.V. 1. Introduction At present thousands of synthetic dyes are being used in textile, pharmaceutical, cosmetics, food and beverage processing, solar cells, paper making, and computer industries. They also find wide applications in biological sample imaging. Many of these dyes having intense color are being discharged in water bodies. Around 10–15% of the manufactured dyes are lost every year. These col- ored dyes pollute both surface water and ground water. Many of them are non-biodegradable under normal environmental condi- tions, and show mutagenic, carcinogenic and micro toxic behavior. As a consequence they affect biota and human beings. Although various technologies are developed for the removal and treatment of dye contaminated water and wastewater, but they have their own limitations. For example, the biological treatments [1,2] may be suitable for decolorizing the dyes effectively, but in many cases the intermediates produced during the degradation are more toxic than the mother compound. Malachite green (MG) is a cationic dye used worldwide as a biocide in the aquaculture industry. The usefulness of MG against protozoan and fungal infection is very well-known. Although it is a therapeutic agent for tropical treatment in fishery, but it is potent enough to produce significant internal effects through systematic adsorption on fishes. It mainly works as an ectoparasiticide in aquaculture industry. The other applications of MG are as a food additive, coloring agent, medical disinfectant and antihelminthic. Application of MG in silk, wool, jute, leather, cotton, and paper industries is also enormous. The toxic effects of MG have been studied widely [3,4]. The carcino- genic effects in immune and reproductive system, and genotoxicity was observed due to the consumption of MG treated fishes [5,6]. This caused the dye to be banned in many countries. Recently the US Food and Drug Administration have designated MG as a pri- ority chemical for carcinogenicity testing. In spite of all these facts this dye is still being used in many countries due to its low cost, easy availability and efficaciousness [7]. The reduced MG i.e. leuco- malachite green (LMG) is not only considered as a contaminant in aquatic and earthly ecosystems, but also it is recognized as a potential hazard for human health. During the treatment of fungal and parasitic infection in fishes, MG is reduced to LMG and adsorbed in the exposed tissues like liver, kidney, muscle, skin and viscera [8–13]. Recently nanomaterials have found wide applications as cata- lyst [14–16]. These fine particles have very large surface area and they offer special binding sites to the reacting species. This makes them active for various types of homogeneous and heterogeneous http://dx.doi.org/10.1016/j.seppur.2014.07.021 1383-5866/Ó 2014 Published by Elsevier B.V. ⇑ Corresponding author. Tel.: +91 3222 281920; fax: +91 3222 282254. E-mail address: anjalipal@civil.iitkgp.ernet.in (A. Pal). Separation and Purification Technology 134 (2014) 26–36 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur