**1. Introduction**

The development of the chemical industry has resulted in large-scale pollutant emission, which has brought about a series of environmental problems [1]. Organic dyes, in particular, are highly toxic and chemically stable, potentially teratogenic, and carcinogenic to humans [2]. As a "green" technology, photocatalysis has attracted widespread attention because it can efficiently degrade dyes to avoid its pollution to the environment [3,4].

Titanium dioxide (TiO2) is considered one of the most promising photocatalysts because of its advantages of good chemical stability, nontoxicity, and low cost to degrade organic pollutants in the field of printing and dyeing [5,6]. However, TiO2 has a wide band gap (3.0–3.2 eV) and excitation light is limited to ultraviolet light (4%), which greatly decreases its utilization efficiency of solar energy [7]. In addition, TiO2 nanoparticles exhibit a low specific surface area, easy aggregation, and poor recycling, which limit its application range [8]. Therefore, improving the adsorption capacity and photocatalytic performance of TiO2 is important.

Smectite clay is a layered silicate mineral with a high adsorption capacity and specific surface area, and some composite clay materials can change the phase of semiconductors or improve the separation of e<sup>−</sup> and h+, which can be used to support TiO2 [9]. The interlayer cations in the composite clays tend to capture electrons and oxidize the holes, thus reducing the charge recombination rate and improving the photocatalytic performance. Hectorite belongs to 2:1-type layered clay composed of a Si–O tetrahedron and a Mg–O octahedron arranged in 2:1 order in the vertical direction, and its molecular structure is Mx[LixMg6−xSi8O20(OH)yFz] ( M = Na, Li) [10,11]. Hectorite can facilitate the separation of composites and improve the recycling of catalysts [12]. Therefore, TiO2/hectorite composite

material with high photocatalytic performance can be prepared by utilizing the adsorption and ion exchange properties of hectorite to enhance the degradation rate of dye wastewater.

The composite of clay and TiO2 has the advantages of small titanium crystal size, large porosity, and large specific surface area [13]. However, it is usually difficult for TiO2 to enter the interlayer. Moreover, due to the wide band gap of TiO2, TiO2/clay composites have photocatalytic activity only under ultraviolet light [14]. Up until now, TiO2/hectorite has been synthesized mainly by the hydrothermal method, sol-gel method, and hydrolysis method [15–17]. In previous studies, most of them reacted by mixing TiO2 precursor solution with the suspension of hectorite directly. The process is complicated and takes a long time. Furthermore, it is difficult for TiO2 to enter the interlayer of hectorite, which limits the photocatalytic activity [18]. Ma et al. synthesized TiO2/hectorite and found the influence of titanium content on photocatalytic performance [19]. However, TiO2 was usually only supported on the mineral surface, not in the interlayer space of hectorite. It is worth studying TiO2/hectorite composite materials by utilizing the exchange ability of the interlayer cation to introduce titanium ions into the interlayer during the synthesis of TiO2/hectorite. Therefore, we studied the synthesis of TiO2/hectorite nanocomposites as photocatalysts at different molar ratios of lithium, magnesium, and silicon prepared by a simple one-pot hydrothermal method and utilization for the photodegradation of MB under UV light irradiation.
