Sustainable "waste-treat-waste" strategy for constructing Ni(OH)2/carbonized halloysite nanotubes: Enhanced adsorption and interactive mechanism for methyl orange

Methyl orange was in-situ converted into carbon layers on HNTs. • Carbonization and alkali-etching realized the interface engineering and pore regulation. • HNTs framework prevented the agglomeration of Ni(OH) 2 nanosheets. • The composite removed 98.1% of MO and achieved a maximum capacity of 380.7 mg g −1 within 5 min. In this study, carbonized halloysite nanotubes were obtained by thermal treatment of methyl orange (MO)-coated HNTs followed by alkali activation, which were then used as supports to construct a series of Ni(OH) 2 /carbonized halloysite nanotube composites (denoted as NCHB x - y ) to further remove MO. The as-prepared adsorbent NCHB 0.5 -500 could remove over 98.1% of MO (40 mg L −1 ) and achieve a maximum adsorption capacity of 380.7 mg g −1 within 5 min. Notably, NCHB 0.5 -500 exhibited the strong adaptability to pH and temperature variations, along with the excellent selectivity and versatility in six-mixed-dyes and multiple-anions systems. The adsorption mechanism studies indicated that the tubular HNTs served as a robust framework to prevent Ni(OH) 2 agglomeration, while the alkali-etching constructed a rich mesoporous structure and the in-situ MO modification enriched surface functional groups and introduced π-π stacking interactions. These structural advantages combined with hydrogen bonds and electrostatic attraction synergistically enhanced the interaction between the adsorbent and MO molecules, thereby improved the adsorption performance. This study develops a recommendable method for constructing high-performance and low-cost adsorbents based on clay minerals for wastewater treatment and contributes a sustainable "waste-treat-waste" strategy for functionalizing natural clay minerals. In-situ MO modification and alkali-etching for HNTs contributed to a rich mesoporous structure and enriched surface functional groups, both of which were favorable for enhancing the adsorption efficiency. Download: Download high-res image (306KB) Download: Download full-size image