Ag2O-adorned ZnO nanostructures: cooperative and sustainable nanomaterial system for effective reduction and mineralization of hazardous water pollutants

Abstract

Organic water pollutants like nitroaromatics and synthetic dyes are causing serious threats to water. Ever-growing urban and industrial activities along with population explosion are rapidly contributing severe level of water contamination. Semiconducting nanomaterial-based photocatalysis has been proven to be an effective process for degradation of organic water pollutants. In the current study, visible light active Ag2O-adorned ZnO nanostructures were fabricated by a simple two-step hydrothermal method and the prepared nanostructures were utilized for the photocatalytic mineralization of rhodamine B (RhB) dye with visible light radiation. The catalytic potential of as-synthesized nanostructures was also investigated for the reduction of nitroaromatics (4-NP and 4-NA) and RhB dye in the presence of NaBH4. The Ag2O-adorned ZnO nanostructures prepared with 5% of silver nitrate denoted as ZnO/Ag2O (5%) demonstrated stupendous photomineralization activity against RhB dye as almost 100% degradation of RhB dye was achieved within 100min of reaction time at pH = 6. The kinetic study revealed that the degradation reaction followed the pseudo-first-order kinetics and the kinetic rate constant (k) of photodecolorization reaction for optimal catalyst was calculated to be 61.4 × 10-3min-1. The nanostructures revealed excellent recyclability and photostability as 95% activity of the catalyst was preserved even after the fifth cyclic run. The catalytic reduction of the 4-NP, 4-NA, and RhB dye was completed in 21, 12, and 40min, respectively, in the presence of ZnO/Ag2O (5%) and NaBH4 solution. The kinetic rate constant values for the reduction reactions were determined to be 229.6 × 10-3, 454.2 × 10-3, and 105.5 × 10-3min-1 for 4-NP, 4-NA, and RhB dye, respectively. Thus, the obtained results suggest that the components of the prepared nanosystem help in mutually strengthening the catalytic and photocatalytic abilities of each other, indicating the development of a cooperative and sustainable nanomaterial system in the current study.