Synthesis, characterization, and adsorptive performance of titanium dioxide nanoparticles modified groundnut shell activated carbon on ibuprofen removal from pharmaceutical wastewater

Abstract

In this study, Titanium dioxide Nanoparticles (TiO2 NPs) were biosynthesized using the extract of Cola nitida (Kola nut) pod as a reducing agent. The synthesized TiO2 NPs were impregnated on the surface of Groundnut Shell Activated Carbon (GNSAC) to produce TiO2-NPs-GNSAC, and its performance on the removal of ibuprofen from pharmaceutical wastewater was investigated. The two adsorbents (GNSAC and TiO2-NPs-GNSAC) were characterized using proximate analysis, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), Brunauer-Emmett-Teller (BET), and Energy Dispersive X-ray (EDX). Physical properties such as moisture content, ash content, and volatile matter content were also determined. The combined effects of three independent variables (temperature, time, and adsorbent dosage) were evaluated in a batch study designed through Box Behnken Design (BBD) of the Response Surface Methodology (RSM) for experimental design, analysis, and process optimization. Regeneration examinations were conducted for three cycles. The proximate analysis showed that GNSAC and TiO2-NPs-GNSAC have 63.21 and 71.11 % of carbon, respectively, which could be attributed to the high organic content in Groundnut Shell (GNS). BET analysis proved that the adsorbents (GNSAC and TiO2-NPs-GNSAC) were mesoporous with mean pore sizes of 6.046 and 5.353 nm, respectively. At optimum conditions of 0.62 g/L, 30 °C and 30 min for adsorbent dosage, temperature, and time, respectively, 68.53 % of ibuprofen was removed using GNSAC, while 81.78 % of ibuprofen was removed at optimum adsorbent dosage, temperature, and time of 0.5 g/L, 30 °C, and 50 min, respectively, using TiO2-NPs-GNSAC. Langmuir isotherm best described the equilibrium data using GNSAC and TiO2-NPs-GNSAC, with maximum monolayer adsorption capacities of 40.82 mg/g and 55.56 mg/g, respectively. Pseudo second-order kinetic model was more suitable to predict the experimental data. The mean free energy (E) values of 0.345 and 0.746 KJ/mol obtained for ibuprofen adsorption onto GNSAC and TiO2-NPs-GNSAC indicate that the mechanism of adsorption of ibuprofen follows the physisorption process. Based on the thermodynamic investigation of the current process, it can be concluded that the adsorption of ibuprofen by the prepared activated carbon (GNSAC and TiO2-NPs-GNSAC) was a spontaneous and endothermic process. Additionally, the adsorbent was successfully regenerated three times, and it was able to perform the adsorption and desorption processes well. Hence, the results of this work suggest that the activated carbon prepared from groundnut shell is a suitable adsorbent for the adsorption of ibuprofen from pharmaceutical wastewater.