Effective Catalytic Reduction of 4-Nitrophenol to 4-Aminophenol over Etched Halloysite Nanotubes@α-Ni(OH)₂

A series of supported α-Ni(OH)2 structures on etched halloysite nanotubes (eHAs) are synthesized via a one-pot facile co-precipitation method. By expediently controlling the variety of alkali source, etched halloysite nanotubes@α-Ni(OH)2 (eHA@α-Ni(OH)2) with different α-Ni(OH)2 morphologies and Ni2+-ion contents can be achieved. The prepared eHA@α-Ni(OH)2 is used to catalytically reduce 4-nitrophenol (4-NP). It shows that eHA@α-Ni(OH)2 prepared with n-butylamine as an alkali source (eHA@α-Ni(OH)2-B) exhibits a higher kapp of 1.458 × 10–2 s–1 and K of 583.27 s–1·g–1. The catalytic reduction property is in accordance with the Ni2+-ion content of eHA@α-Ni(OH)2. Moreover, it also exhibits a good cycle stability due to the synergy of the support eHA and the supported Ni2+ ions in α-Ni(OH)2, which can achieve a 99% 4-nitrophenol conversion after 11 cycles. The Ni2+-ion reduction experiment illustrates that the Ni2+ ion is the activation site and the enhanced 4-NP reduction activity of eHA@α-Ni(OH)2-B is attributed to the higher Ni2+-ion content, which accelerates the electron transport from NaBH4 to 4-NP to result in the catalytic reduction of 4-NP to 4-aminophenol (4-AP).