Synthesis of amine-modified zeolitic imidazolate framework-8, ultrasound-assisted dye removal and modeling

The present research is focused on the ultrasound assisted adsorption of Acid blue 92 (AB92) and Direct red 80 (DR80) as anionic dyes in single and binary systems onto zeolitic imidazolate framework (ZIF-8) functionalized with 3-Aminopropyltrimethoxysilane (APTES). Different techniques such as Fourier transform infrared (FTIR), scanning electron microscope (SEM), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and thermogravimetric analyses (TGA) were used to characterize the prepared adsorbent. The individual effects and possible interactions between the various parameters including adsorbent dosage, sonication time, initial dye concentrations and pH on dyes removal efficiency were investigated by response surface methodology (RSM). The optimized experimental conditions were fixed at adsorbent dosage 0.005 g for AB92 and 0.01 g for DR80, pH 2.1, sonication time 15 min, and initial dyes concentration 15 mg L−1 to get maximum removal percentage (>95.0%). A reliable and intelligent model based on least-squares support vector machine (LS-SVM) was developed to predict dye removal efficiency. The root mean square error (RMSE) of 0.604, 0.734 and 1.549 with high determination coefficient (R2) of 0.999, 0.996 and 0.997 for AB92, DR80 and binary system, respectively, were able to predict and model the adsorption process. The presented model illustrates better performance in predicting dye removal efficiency compared to the kinetic models. The results showed that the adsorption process had better conformation with pseudo-second order model. The adsorption equilibrium data was investigated by Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich isotherm models and the data were well fitted by Langmuir model with maximum adsorption capacity of 633.4 and 500.2 mg g−1 for AB92 and DR80 dyes, respectively. APTES@ZIF-8 was regenerated and found to be reusable after four successive cycles without considerable loss in adsorption capacity.