Probing Environmental Remediation of RhB Organic Dye Using α-MnO₂under Visible- Light Irradiation: Structural, Photocatalytic and Mineralization Studies

Abstract

Photocatalytic activity of α‐MnO2 nanorod synthesized through a low temperature (90 °C) single step precipitation route in the absence of surfactant and template is reported. Dependence of precipitation time on morphology of the synthesized α‐MnO2 has been investigated and the photocatalyst has been tested for the degradation of organic cationic and anionic dyes. Detailed study on the degradation of Rhodamine B (RhB) has been carried out. The lower precipitation time (of 6 h) is found to be ideal for the synthesis of the photocatalyst. The mechanism of RhB photodegradation under visible light using α‐MnO2 nanorods has been established through mass spectra analysis. The intermediate products during degradation exhibits de‐ethylation and mineralisation steps. Experimental results suggest that both super oxide and hydroxyl radicals are the main active species in the process. Total organic carbon (TOC) analysis of treated RhB reveals complete mineralisation. The photodegradation efficiency of α‐MnO2 for cationic and anionic dyes are found to be 95–100 % under visible light irradiation. The excellent photocatalytic activity of α‐MnO2 can be correlated with its 1‐D morphology of high aspect ratio and low photoluminescence intensity. The complete dye discoloration within 10 min and total mineralisation of RhB in 25 min is quite significant especially under visible light irradiation and has never been reported earlier.

Multi-functional MnO2 nanomaterials for photo-activated applications by a plasma-assisted fabrication route

“…4,30,32,56 As a general rule, all specimens were active in the target process and the dye decomposition followed a pseudo-firstorder reaction kinetics, as usually reported in similar cases. 5,6,34 The values of apparent first-order rate constants and half-life are reported in Fig. 8d.…”

“…[1][2][3] In particular, great attention has been devoted to the degradation of persistent pollutants in effluent wastewaters, such as dyes from textile, paper and pharmaceutical industries, into harmless products. [4][5][6] In addition, increasing efforts have been focused on photoinduced anti-fogging and self-cleaning appli-cations promoted by suitable functional systems, for which surface adsorption phenomena and hydrophobic/hydrophilic properties directly affect functional performances. 7,8 Among the possible candidate materials, MnO 2 is an important transition metal oxide possessing various polymorphs, such as α-, β-, γand δ-MnO 2 , [9][10][11][12][13][14][15][16][17][18] and has been the subject of several studies.…”

“…31 Therefore, MnO 2 -based systems could be usefully exploited in curbing environmental pollution and promoting water purification and safety, thanks also to their low toxicity, moderate price and high activity. 6,15,[32][33][34] So far, MnO 2 materials have been used for the photodegradation of organic dyes in wastewater. 1,5,6,11,13,34 In a different way, reports on the reversible hydrophobic/hydrophilic switching and on solid phase photoactivated pollutant degradation have been devoted to TiO 2 4,35,36 and other oxide materials, 7,8 but, to our knowledge, no MnO 2 -based systems have ever been investigated for such applications.…”

“…12,16,33 As a consequence, efforts have been dedicated to the fabrication of low-dimensional MnO 2 systems using various techniques, 29,34,39,40 among which liquid-phase routes are by far the most used. 6,9,11,14,16,32 However, several studies have been dedicated to powders, 5,9,10,12,26,30,40 whereas supported MnO 2 systems, though being undoubtedly preferable for various applications, 7,36,41,42 are indeed much less investigated. 2,20,21,43 In particular, although previous studies have been done on nanostructured β-MnO 2 as an electrode, as well as catalytic and magnetic materials, 16,17,22,[37][38][39]43,44 the functional investigation of this polymorph, especially in supported forms and for photoactivated applications, deserves further efforts.…”

“…2,20,21,43 In particular, although previous studies have been done on nanostructured β-MnO 2 as an electrode, as well as catalytic and magnetic materials, 16,17,22,[37][38][39]43,44 the functional investigation of this polymorph, especially in supported forms and for photoactivated applications, deserves further efforts. 6 Herein, we report the preparation of phase-pure supported β-MnO 2 nanomaterials, whose applications in Vis-light photoactivated processes are scarce, by means of plasma-enhanced chemical vapor deposition (PE-CVD), exploiting the unique gas-phase and surface chemistry of cold plasmas. 8,45 So far, only one work is available on the PE-CVD of MnO x thin films, but the control of phase composition has been proven to be difficult.…”