The 2,2'-(pentane-1,5-diylbis(oxy))dibenzaldehyde (BP) functionalized silica gel (Si-APTES-BP) was synthesized successfully by a normal method and a inverse method. These new materials were characterized by Fourier Transform Infrared (FT-IR), Scanning Electron Microscopy (SEM), Thermogravimetric Analyzes (TGA) and Ultraviolet Visible (UV-vis). The modified silica gel with normal method was used as a sorbent for removal of anionic reactive dyes Reactive Blue 19 (RB19) and Reactive Yellow 84 (RY84) from their aqueous solutions by batch adsorption procedure. The batch adsorption experiments were performed to study the effect of various experimental parameters such as the solution pH, contact time, initial dye concentration, adsorbent dose and temperature. The results showed that the adsorption capacity of RB19 and RY84 dyes were enhanced with increase temperature of solution. The maximum uptake value for RB19 and RY84 dyes were obtained at pH 5 and pH 8, respectively. The isotherm data of both investigated dyes were analyzed by the Langmuir and Freundlich adsorption models. Based on the correlation coefficient values, it has been deduced that the Langmuir model is better fitted to the experimental data. The Langmuir maximum adsorption capacity of the Si-APTES-BP at 298 K was found to be 37.45 for RB19 and 32.36 mg/g for RY84, respectively. In addition, thermodynamic studies were conducted to calculate the changes in Gibbs free energy (Delta G degrees), enthalpy (Delta H degrees) and entropy (Delta S degrees). The negative values of Delta G degrees and the positive value of Delta H degrees indicated that the adsorption process of both investigated dyes was a spontaneous and endothermic process in nature. The reusability of Si-APTES-BP has proven that the adsorbent is durable and cost-effective. Therefore, the silica gel modified with 2,2'-(pentane-1,5-diylbis(oxy))dibenzaldehyde can be used as an effective adsorbent for the removal of anionic reactive dyes from aqueous solutions. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.