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Abstract In this work, a novel rhombic dodecahedral structure of Ca-Al-layered double hydroxides (Ca-Al-LDHs) was synthesized by a two-phase solvothermal method. Subsequently, Ca-Al layered double oxides (Ca-Al-LDOs) were obtained by calcinating Ca-Al-LDHs at 600 °C which maintained the rhombic dodecahedral structures well. The morphologies of as-obtained samples were characterized by both transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The phase structure and elemental composition were analyzed by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), respectively. Fourier transformed infrared (FT-IR) spectra were performed to confirm the existence of LDH structures. The Ca-Al-LDOs exhibited high adsorption rates and superb adsorption capacities for removal of Congo red (CR) from aqueous solution. The maximum adsorption capacities of Ca-Al-LDOs towards CR reached to 1536.1 mg g−1, which is extremely higher than most of hydrotalcite-like materials. The adsorption process of Ca-Al-LDHs and Ca-Al-LDOs were described by the Langmuir isotherm model and pseudo-second-order model well. The adsorption mechanisms mainly dominated by electrostatic adsorption, ion exchange process, hydrogen bonding interactions and surface complexation. This general strategy afforded a wide possibility to prepare a novel and advanced LDOs adsorption material for water treatment. Graphical abstract Image 1 Highlights • Ca-Al-LDHs were synthesized via a two-phase solvothermal method. • Ca-Al-LDHs and Ca-Al-LDOs with rhombic dodecahedral morphology. • The Ca-Al-LDOs has the maximum adsorption capacity of 1536.1 mg g−1. [ABSTRACT FROM AUTHOR]