Dissolution studies on TiO2 with organics

In this work the effect of organic reducing reagents, namely, ascorbic acid, oxalic acid and l-cysteine on dissolution of commercial TiO2 has been investigated. Kinetic studies showed that a maximum of about 45% of TiO2 was dissolved by ascorbic acid in 4 h when oxide:acid molar ratio was kept at 1:2. The dissolution of TiO2 increased with increase in ascorbic acid and oxalic acid concentration up to 0.15 M in 4 h (corresponding to molar ratio of oxide to acid of 1:3) and further addition did not affect the dissolution. Nearly 45% TiO2 dissolution was obtained with ascorbic acid alone while oxalic acid yielded 40% dissolution. When oxalic acid was added along with ascorbic acid in equi-molar concentrations, dissolution of TiO2 was enhanced to 60% in 2.5 h but when cysteine was added to ascorbic acid the dissolution was about 50% in just 1 h.