Manickavachagam Muruganandham

Recent Developments in Homogeneous Advanced Oxidation Processes for Water and Wastewater Treatment

This paper reports on recent developments in homogeneous Advanced Oxidation Processes (AOPs) for the treatment of water and wastewater. It has already been established that AOPs are very efficient compared to conventional treatment methods for degradation and mineralization of recalcitrant pollutants present in water and wastewater. AOPs generate a powerful oxidizing agent, hydroxyl radical, which can react with most of the pollutants present in wastewater. Therefore, it is important to discuss recent developments in AOPs. The homogeneous AOPs such as O3, UV/O3, UV/O3/H2O2, and UV/H2O2, Fe2

Disinfection of water using Pt- and Ag-doped TiO2 photocatalysts

In this article we have reported heterogeneous photocatalytic disinfection using pristine and Ag- and Pt-doped nano TiO2 under near-UV light and solar light irradiation. Disinfection experiments were conducted in slurry reactors with Escherichia coli, artificial light and sunlight. The influence of various amounts of Pt and Ag loading (0.5% to 5%) on the E. coli inactivation was examined and results indicated that 5% Pt-TiO2 and 0.5% Ag-TiO2 showed the highest photocatalytic E. coli inactivation. The Pt- and Ag-doped photocatalysts were characterized using XPS and TEM analysis. The influence of experimental parameters such as various photocatalysts, photocatalyst concentration, reactor geometry effect, pH and temperature on the photocatalytic disinfection was studied. The experimental results show that sunlight or near-UV light with TiO2 photocatalyst strongly inactivates E.coli. The Ag-TiO2 photocatalyst was the most efficient photocatalyst tested for bactericidal activity. A plausible mechanism of photocatalysed E. coli inactivation is discussed. In conclusion, the doped nano TiO2 photocatalysts is a potential candidate for E. coli inactivation.

Reagents for ZnS Hierarchical and Non-Hierarchical Porous Self-Assembly

Monodispersed highly ordered and homogeneous ZnS microsphere with precisely controlled hierarchical and non-hierarchical surface structure was successfully fabricated in water-ethanol mixed solvent and in water without using any catalysts or templates in a hydrothermal process. The microsphere formation has been facilitated by self-assembly followed by Ostwald ripening process. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDX). The XRD results indicated that the cubic phase ZnS formed in hydrothermal process at various reaction times. Introducing ethanol as a co-solvent with water facilitated hierarchical porous surface structure. The influences of various zinc and sulfur precursors, various alcohols as co-solvent, and solvent ratio on the formation of specific surface structured microsphere was investigated. The water-ethanol (1:1) solvent ratio is the minimum required to facilitate hierarchical porous surface structure. The by-products formed during the hydrothermal process are induced specific surface structure in ZnS microsphere. This is the first report on in situ generated by-products being used as a reagent to facilitate surface structured material fabrication. The formed by-products could be used as recyclable reagents to fabricate hierarchical porous ZnS in three consecutive cycles. A plausible growth mechanism of by-product-induced surface structure in different solvent was discussed. The research results may lay down new vistas for the in situ generated by-product-assisted specific surface structured ZnS fabrication.

Development of high efficiency silica coated β-cyclodextrin polymeric adsorbent for the removal of emerging contaminants of concern from water

This article reports the removal of several emerging contaminants (ECs) from water using novel adsorbent comprising of β-cyclodextrin (β-CD) coated on silica. Fourteen different adsorbents were synthesized under different experimental conditions using two different crosslinking agents (hexamethylene diisocyanate (HMDI) and epichlorohydrin (EPI)) and co-polymers (glycidoxypropyl trimethoxysilane (GPTS) and aminopropyl triethoxysilane (APTES). The adsorption capacities of the synthesized adsorbents were initially evaluated using 17β-estradiol, perfluorooctanoic acid (PFOA), and bisphenol-A (BPA) as adsorbates. The adsorbent prepared by using HMDI as crosslinking agent with DMSO as solvent was observed to perform the best, and removed more than 90% of 17β-estradiol, PFOA, and BPA. Furthermore, the β-CD loading on the ECs removal was studied which showed that the adsorbate removal increases with increase in loading of β-CD on the substrate. The best adsorbent was resynthesized in seven batches and its performance was reproducible for the removal of ten steroid hormones. The adsorbent showed very good regeneration potential for four successive adsorption-regeneration cycles to remove steroid hormones and PFOA. A plausible mechanism of adsorption is proposed. The synthesized best adsorbent is characterized using FTIR, HR-TEM, TGA and nitrogen adsorption analysis. The TGA results showed that the adsorbent has thermal stability of upto 300°C.

Are dopant-stabilized visible light-responsive photocatalysts efficient and stable?

Nitrogen and carbon codopants-stabilized hierarchical porous ZnS microspheres undergo an unexpected dynamic transformation into hollow microspheres when nitrogen and carbon are removed from the former. Thus, such a transformation is evidence for the unprecedented stability of non-metal doped visible light-responsive photocatalysts.

Facile synthesis of self-assembled biporous NiO and its electrochemical properties

In this article, we report the synthesis of self-assembled bi-porous nickel oxide on a large scale without using any templates or matrix. Porous NiO microspheres composed of particles were obtained by thermal decomposition of nickel oxalate, which was prepared using nickel salt and oxalic acid as precursors. The as-obtained nickel oxalate and nickel oxide were characterized using X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), thermogravimetric analysis (TGA), and nitrogen adsorption-desorption analysis. The influence of various experimental conditions on the formation nickel oxalate and NiO were studied. The nitrogen adsorption-desorption analysis showed that the synthesized NiO possesses a biporous (both mesoporous and macroporous) surface structur. The NiO microspheres showed a discharge capacity of 2929 mAh g−1. A plausible mechanism for the NiO self-assembly was proposed.

Novel Sampling for the Determination of Naphthalene in Air by Gas Chromatography–Mass Spectrometry

ABSTRACT Here are reported two new sampling method approaches for the determination of naphthalene in ambient air for concentrations from 0.25 to 18.7 µg/L. The first method used for gas phase naphthalene analysis produced an average recovery of 88.8% and the second method using headspace sampling produced an average recovery of 93.8%. The second method showed better recovery than the former, so it was used for subsequent comparative gas-phase determination of naphthalene. The second method was validated at various naphthalene concentrations and humidity using a naphthalene gas generator to produce various naphthalene standards and a naphthalene-monitoring instrument. The naphthalene concentrations generated using the gas generator and determined second sampling method with gas chromatography–mass spectrometry (GC–MS) were compared to the sensor measurements and were in good agreement. In summary, the sampling methods presented provided reliable gas-phase naphthalene determination when coupled with GC–MS.