Methyl orange (MO) is a common anionic azo dye that is harmful to the environment and biology, so it must be treated innocuously before it can be discharged. Adsorption is an effective method to remove anionic dyes. Nanotube mineral is a natural one-dimensional adsorption material, and its unique morphology and structure endow it with good adsorption capacity. Although there are many related studies, there is a lack of in-depth discussions on the influence of nanotube’s composition and structure on the adsorption of dyes and other pollutants. In this paper, two kinds of natural one-dimensional silicate minerals [halloysite nanotubes (HNTs) and chrysotile nanotubes (ChNTs)] with similar morphology but slightly different compositions and crystal structures were used as adsorbents, and MO solution was used as simulate pollutants. It is the first time to discuss in depth the influence of the composition and structure of nanotube minerals on their charge properties and the adsorption performance of methyl orange dyes. It is found that HNTs and ChNTs have different adsorption capacity due to the difference of electronegativity between Al³⁺ and Mg²⁺ in the crystal, so they possess negative and positive charges respectively in near-neutral solution, which leads to the adsorption capacity of MO by ChNTs with positive charges which is greater than that of HNTs.

As most heavy metals are highly toxic upon accumulation in the human body, it is urgent to develop accurate, low-cost, and on-site methods to detect multiple heavy metal ions in real water samples. Quantum dots (QDs) are an approved choice for use in sensors and exhibit favorable luminescence in aqueous solution, but they often become quenched when isolated from their suspensions due to agglomeration. Therefore, QDs must exist in a solid state in order to be successfully applied to luminescence detection. This work reports the fabrication of a novel luminescence composite based on glutathione-capped Mn-doped ZnS quantum dots (GSH-Mn-ZnS QDs) and layered double hydroxides (LDH). The composite is solid and exhibits enhanced luminescence intensity, as the structure of LDH prevents the aggregation of QDs. Most importantly, it exhibits a similar response when used as a sensor for detecting Pb²⁺, Cr³⁺ and Hg²⁺ with a linear range of 1 × 10⁻⁶ M to 1 × 10⁻³ M for each heavy metal, and a detection limit for the mixed metal ions of 9.3 × 10⁻⁷ M. In addition, the composite was successfully applied for detection in lake water with low interference. Therefore, a practical method is presented for the design and fabrication of a QD–LDH composite that can be used for qualitative and quantitative testing of mixed heavy metal ions simultaneously in real water samples.