The TiO2 nanoparticles were purchased from Degussa P25
(Evonik Degussa GmbH, Düsseldorf, Germany) with a purity
>99.5%. Degussa P25 TiO2 has a reasonably well defined nature,such as an anatase: rutile mixture with a ratio of 80:20, non-porous
material, and BET surface area of 55.0 ± 15.0 m2 g1. The prime
particle size of the TiO2 nanomaterial is approximately 20.0 nm.
The black crystalline humic acid powder was obtained from SigmaeAldrich
Company. The HA stock solution was prepared by
dissolving a certain amount of HA powder in Milli-Q water, and the
concentration was controlled to be 0.5 g/L while the pH was 7.1.
After being stirred for 24 h, the solution was filtered through
0.22 mmmembranes under vacuum. All of the other chemicals were
analytical reagent grade and used as received without further purification.
The water used in the preparation of this solution was
Milli-Q® element ultrapure water (Integral 15). The glassware was
immersed in a 5% HNO3 solution for 24 h, washed thoroughly with
Milli-Q® water, and dried at 333 K before use.