Promotion effects of halloysite nanotubes on catalytic activity of CoO nanoparticles toward reduction of 4-nitrophenol and organic dyes.

Nanosized clay minerals have been widely used as efficient supports to immobilize catalyst nanoparticles. However, clay support-induced interactions and their influences on the catalyst structure and performance currently have not been fully understood. Here, CoO nanoparticles supported on halloysite nanotubes (HNTs) were synthesized by a facile deposition-precipitation approach followed by thermal treatment. A series of characterization methods were employed for the CoO/HNTs hybrid nanostructure to identify its crystal phase, chemical composition, morphology, specific surface area, surface chemical states, and redox property. Characterization results showed that HNTs not only impacted the particle size of CoO nanoparticles, but also modified surface chemical surface states of the later, which ultimately promoted the effective catalytic reduction of 4-nitrophenol (4-NP) and azo dyes with sodium borohydride. The interaction between HNTs and CoO nanoparticles was found to shorten the induction period of the 4-NP reduction. Meanwhile, the CoO/HNTs catalyst for the 4-NP reduction achieved an apparent rate constant of 0.265 min and an activity parameter of 1.63 × 10 min g as well as a turnover frequency of 4.37 min. In addition, CoO/HNTs showed an improvement in reduction efficiency of the azo dyes when compared to bare CoO nanoparticles.