(762b) Catalytic Oxidation of Arsenic (III) Over Manganese Doped Titania Nanotubes in WATER

Arsenic is a well known toxic and carcinogen. A perilous arsenic concentration in natural waters is now a global problem and often considered as a 21^st century calamity. Dangerous arsenic concentrations have been reported recently from different parts of the world with the largest population at risk in Bangladesh and West Bengal, India. Studies of arsenic removal from water using metal oxides and clay minerals have recently been developed. Manganese-bearing materials have shown promising performance in this field. A novel method has been developed for the preparation of manganese doped titania nanotubes (Mn-TNTs) using solution combustion synthesis and the hydrothermal method. Combustion synthesis has emerged as a hassle-free and economically viable technique for the preparation of advanced ceramics, catalysts, and nanomaterials. Stoichiometric amounts of transition metal nitrates and Glycine were mixed in a solution for the preparation of nanoparticles at 350° C in a single step. The thus prepared Mn_xTi_1-xO_(2-δ) (x = 0.1 to 0.3) nanomaterials are in the anatase phase. The nanotubes were then fabricated via the hydrothermal method using 10 N NaOH at temperature of 130°C for 24 hours.

The morphology was observed using a JEOL 2100 field emission Gun Transmission Electron Microscope (JEM 2100F TEM) and HITACHI S-3400 N Scanning Electron Microscope (SEM) attached with Energy Dispersive X-ray Spectrometry (EDX). X-ray diffraction (XRD) analysis was performed on a Bruker D8 Focus diffractometer equipped with a Sol-X detector using a copper radiation source. Specific surface area analysis was done using the Brunauer, Emmett, and Teller (BET) method based on N₂ adsorption at 77 K with a NOVA 1000 series analyzer.  

Mn-TNTs (Mn_0.1Ti_0.9O_(2-δ) , Mn_0.15Ti_0.85O_(2-δ) , Mn_0.2Ti_0.8O_(2-δ) , Mn_0.25Ti_0.75O_(2-δ) , Mn_0.3Ti_0.7O_(2-δ)) were tested and compared for the oxidation of Arsenic(III) in water. With a catalyst loading of 200 mg/L, the suspension was stirred using a mechanical stirrer. As(III) and As(V) were analyzed using Nano-Band™ Explorer II and Manganese was analyzed using Specrto Genesis ICP-OES. There was no manganese present in the liquid media, which means manganese neither dissolving nor reacting with the As(III). Hence, Mn-TNTs catalyzes the oxidation of dissolved As(III) in water. A second-order rate equation was found to best fit (R2 > 0.99) the kinetic data for all the materials. Oxidation of Arsenic(III) was found to be the highest for the Mn_0.15Ti_0.85O_(2-δ) nanotubes. The reaction rate increases with temperature from 20 to 40°C with an activation energy of 27228 kJ/k-mole.