## 1 Introduction  
The purity of water, due to extensive industrialization, urbanization and agriculture, is critically diminished in many countries due contaminations by dye-based industries such as textiles, paint, plastics, paper, leather and so on. The untreated wastewater containing dyes from these industries are posing a very serious threat to human health and the environment. Therefore, the dye-contaminated wastewater should be treated and dyes removed before releasing it into the environment or reusing it. Among many dyes used in these industries, water-soluble Congo Red (CR) is particularly hazardous and used at high concentrations in textile and biochemistry based industries [1]. This benzidine based dye is very toxic, highly carcinogenic and can lead to serious health issues such as diarrhoea, vomiting and nausea [2]. Many water purification technologies have been developed and are commercially available for the removal of organic dyes from water, including membranes, coagulation, catalysis, ozonation, and adsorption [3; 4; 5]. Among them, the adsorption process is commonly used as it is a very simple, cost-effective, reproducible and effective process for the removal of dyes from water [6]. Manyefficient adsorbents such as activated carbons, polymers and clays were explored and some of them were commercially used for dye removal from water, including CR. However, there is still a strong demand to develop new adsorbents that are environmentally friendly, low cost and, more specifically, efficient for dye adsorption [7]. One such environmental friendly naturally available low-cost material known as diatomaceous earth or diatom (DE) has been well-recognized as an excellent candidate for dye removal applications, with an attractive ability to tune the surface properties of dye and significantly increase its adsorption efficiency. Naturally, available DE materials originating from single-cell algae are found in fresh and sea waters in large quantities. These single cell algae are protected by a unique porous silica shell called the frustule. These hollow DE silica structures have a unique pattern of pores with pore sizes from 100 to 900 nm; also, the size of the DE varies between 1 and 500 \(\upmu\)m. DE is an amorphous silica and is considered non-toxic and biocompatible. It has a high porosity and is lightweight, with high thermal stability and is hydrophilic in nature. These properties make DE as an ideal candidate for the various applications such as waste and drinking water purification, as an additive for composites, drug delivery, pest control, sensors, etc. [8; 9; 10; 11; 12; 13]. However, the fact that bare DE showed less adsorption capacity in the removal of organic dyes could be the reason for the smaller surface area [14] and less hydroxyl groups (-OH) on their surfaces. Therefore, the surface of DE needs further surface modification for better efficiency for the removal of dyes and other pollutants and has been explored by several groups [15; 16; 17]. In the current work, we present a new concept to modify DE material with Mg-Al-layered double hydroxide (DE-LDH) to enhance the dye removal efficiency and adsorption capacity of DE. Layered double hydroxide (LDH) is a mixed-metal hydroxide clay that consists of octahedral double hydroxyl layers with high positive charges, negatively charged interlayers and water molecules [18]. LDH has some advantages such as its low cost, non-toxicity, simplicity, higher adsorption capacity, and has a high thermal stability [19]. Thus, the LDHs are ideal candidates for the removal of organic and inorganic pollutants from water [19; 20; 21; 22]. To the best of our knowledge, this is the first report where DE-LDH has been used for the efficient removal of CR from aqueous media. To study the DE and DE-LDH adsorbents, isotherms were used in the batch adsorption, and kinetic studies were carried out for CR removal. In addition, the obtained maximum adsorption capacity (q\({}_{\text{m}}\)) of DE-LDH has been compared with earlier reported adsorbents.