The abundant natural bentonite from Sarolangun deposit of Jambi Province, Indonesia, has been successfully activated by a wet acid activation method and applied as a low-cost, and environmental-friendly adsorbent for Congo red dye removal from aqueous solution. The activated bentonite samples were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N₂ adsorption-desorption, and X-ray fluorescence (XRF). The batch adsorption technique has been conducted to study the adsorption behavior of Congo red on activated bentonite. The effects of operational parameters toward the Congo red adsorption on activated bentonite, including adsorbent dosage, initial pH, contact time, initial concentration, and temperature were investigated. Moreover, the properties of adsorption kinetics, adsorption isotherm, and adsorption thermodynamic were also investigated. The results of material characterization showed that acid-activated bentonite has better properties than natural bentonite. For instance, the surface area of acid-activated bentonite elevated almost five-fold compared with natural bentonite. The batch adsorption study showed that the Congo red adsorption on acid-activated bentonite was significantly affected by adsorbent dosage, initial pH, contact time, dye concentration, and temperature. The adsorption kinetics investigation revealed that adsorption was best evaluated by a pseudo-second-order model rather than pseudo-first-order model. The adsorption equilibrium study described that the adsorption process followed the Langmuir isotherm model. The result of thermodynamic investigation revealed that the adsorption process occurred spontaneously and favorably in high-temperature conditions.

The Ni–Fe layered double hydroxide (LDH) intercalated by Keggin-type polyoxometalate (POM) of SiW₁₂O₄₀⁴⁻ was investigated for the first time. The synthesized Ni–Fe LDH and Ni–Fe POM were characterized by XRD, FT-IR, and N₂ adsorption–desorption isotherm to identify the intercalation process as well as their surface morphology. The obtained results indicated that after intercalated by POM, the interlayer distance of the LDH expanded due to the insertion of POM anion and removal of some native NO₃⁻ anion in the interlayer space. Moreover, the increment of the BET surface area of the material after intercalation indicated the opening of the interlayer space that beneficial for the adsorption process. The study on the malachite green adsorption onto the synthesized materials showed that POM intercalated LDH has better adsorption capacity than the original LDH, where the adsorption kinetic was better described by pseudo second order model than the pseudo first order model.