Reduction and removal of mercury from water using arginine-modified TiO2

The photocatalytic removal of mercury(II) ions from water was investigated using titanium dioxide (TiO2) nanoparticles (45 Angstrom in diameter) surface-modified with arginine (ARG). TiO2 sols were prepared by the controlled hydrolysis of titanium tetrachloride. ARG-modified TiO2 was placed in water and purged anoxically with an inert gas. Suspensions were spiked with elevated mercury concentrations (from mercuric chloride) and equilibrated for 10 min in darkness (with continuous stirring). Suspensions were either illuminated with 253.7 nm light or kept in darkness while mixing continuously. Samples were periodically withdrawn from the reactor via syringe and filtered anoxically. Precipitate collected on the filters was tested for elemental mercury; filtrate was analyzed for mercury using cold vapor atomic absorption spectrometry. Results showed that in the absence of light, approximately 60% of initial mercury could be sorbed onto the ARG-modified TiO2 [ARG (L67 x 10(-3) M) TiO2 (5.00 x 10(-3) M)]. ARG-modified TiO2 removed greater than 99.9% of the initial mercury (150 ppm) present in solution within 128 min of illumination through sorption and reduction processes. This removal time was reduced to 32 min when methanol was added as a hole scavenger, These sorption and reduction processes were catalytic in nature, The presence of 30 ppm iron(Ill) greatly inhibits both the sorption and the reduction of mercury on ARG-modified TiO2. (C) 2002 Elsevier Science B.V. All rights reserved.