Partial decomposition of NaBiO3 to δ-Bi2O3/NaBiO3 and α-Bi2O3/NaBiO3 heterojunctions in aqueous HAc solution respectively with good adsorption ability and photocatalytic performance

Considering that the construction of heterojunctions could effectively prohibit the recombination of photo generated carriers via interfacial charge transfer in comparison with single-component photocatalytic material, the Bi2O3/NaBiO3 heterojunctions were easily synthesized through the partial decomposition of NaBiO3 in aqueous acetic acid (HAc) solution at room temperature. The phase structures of Bi2O3 could be tuned by the HAc amount. The composite alpha-Bi2O3/NaBiO3 was obtained if the decomposition reaction was conducted with 20 L of HAc (pH = 5.0) for 20 min. As HAc amount increasing, the alpha-Bi2O3 content in the composites was decreased, while the delta-Bi2O3 content was increased, and the products were identified as alpha-Bi2O3/delta-Bi2O3/NaBiO3. When the HAc amount was increased to above 15 mL (pH = 3), delta-Bi2O3/NaBiO3 was generated. Interestingly, the total Bi2O3 content in the composites almost kept constant whether the HAc amount or reaction time was changed. It was proposed that the Bi2O3 coatings were formed on the surface of NaBiO3, which stopped NaBiO3 from further decomposing. Owing to high surface areas and positively charged surface, the as prepared delta-Bi2O3/NaBi3 possessed the high adsorption capacity for methyl orange (MO) with the maximum capacity of 60 mg/g. The adsorption kinetic behavior was well fitted by the pseudo-second order model, and the adsorption process at equilibrium followed the Langmuir isotherm model. Furthermore, the as-obtained alpha-Bi2O3/NaBiO3 exhibited good photocatalytic activity and about 98% of MO was degraded after illuminating for 120 min by visible light. Nevertheless, our designed photocatalyst alpha-Bi2O3/NaBiO3 and adsorbent delta-Bi2O3/NaBiO3 are still far away for practical application for some reasons. Firstly, they are powdery and difficult to recovery, and thus may lead to secondary pollution to water. Secondly, the photocatalytic activity was measured under xenon lamp irradiation, and the activity is still low under natural solar light. Thirdly, the cost of the as designed photocatalyst and adsorbent is not so cheap. Further efforts on the improvement of photocatalysts and photocatalysis technique are underway.