MnO2 AND MnO2/TiO2 MEDIATED, PERSULPHATE ENHANCED PHOTOCATALYSIS FOR THE REMOVAL OF INDIGO CARMINE DYE POLLUTANT FROM WATER

Abstract

Heterogeneous photocatalysis using UV/VIS light or natural solar radiation as the energy source is one of the most efficient advanced oxidation processes (AOP) for the removal of chemical and bacterial pollutants from water. One of the least investigated oxides in this context, i.e. MnO2 and its combination MnO2/TiO2 are examined as potential photocatalysts for the removal of Indigo carmine (IC) dye pollutant from the water. The catalysts are characterized by XRD, FTIR, SEM, TEM, adsorption and surface area measurements. While MnO2 is very efficient for the decolorization of the dye, it is not effective enough for mineralization. MnO2 /TiO2 as the photocatalyst at the optimized ratio of 9:1 combines the advantages of both the oxides, i.e., rapid decolorization and efficient mineralization. Persulphate (S2O8 2-) enhances the degradation while H2O2 inhibits the same. The degradation is dependent on pH with higher degradation under extremely acidic conditions. The influence of dissolved salts/anions in the water on the degradation varies from 'moderate inhibition' to 'no effect' or even 'enhancement' depending on the chemistry of the anion and reaction conditions. Effect of various parameters such as reaction time, substrate concentration, catalyst dosage, the presence of O2, recycling of the catalyst, etc. on the efficiency of degradation is investigated. The results are critically analyzed, and a tentative mechanism is proposed.

MnO2 efficiently removes indigo carmine dyes from polluted water

“…At higher initial concentration (>40 mg/L) the rate remains stable or even slows down slightly thereby demonstrating that the factors favoring degradation of IC under sonolysis are less effective at higher concentration. This also confirms the variable kinetics reported in the case most AOP initiated degradation of water pollutants [ 30 , 57 ]. The optimum rate of degradation under the current experimental condition is 7.5 mg/L/min.…”

“…The effect of pH on the degradation of organic pollutants in presence of semiconductor oxides is often explained based on the point of zero charge (PZC) of the solid [ 8 , 9 ]. The PZC of MnO 2 is ∼4.7 [30] . Below this pH value the surface of the catalyst is positively charged and hence its oxidizing ability will be relatively higher.…”

“…Hence significant amount of O 2 will be present in the MnO 2 /IC suspension, even after long deaeration. Further, it is known that in the case of MnO 2 mediated photocatalytic and microwave catalytic reactions, it functions not only as a catalyst but also as a powerful oxidant [ 29 , 30 ]. The required O 2 is provided primarily by the surface (adsorbed) and lattice of MnO 2 which cannot be easily removed by flushing with N 2 .…”

“…In the present work, a classic heterogeneous catalyst MnO 2 is investigated for its potential as a sonocatalyst for the removal of a recalcitrant dye pollutant Indigo carmine (IC) from water. Only very few investigations aimed at the complete removal of very small concentration of IC from water have been reported and these are mostly based on Advanced Oxidation Processes (AOP), especially photocatalysis and microwave catalysis [ 26 , 27 , 28 , 29 , 30 ].…”

Solution Plasma-Assisted Green Synthesis of MnO2Adsorbent and Removal of Cationic Pollutant

“…Moreover, repetitive generation of abundant OH radicals during discharging (equation 3) could continuously affect the MB degradation. And also, the SP provides UV radiation effect and strong electric fields that are composed of energetic electrons, which could support degradation [32][33][34]. Note that the small plasma zone and weaker radiation energy than the solar simulator limited a radiation range and power, respectively, and thus, we assume that a UV radiation effect plays a subsidiary role in this system.…”