Cu2+-Surface-Modified Activated Carbon from Nutshells for Enhanced Metformin Removal: Mass Transfer Simulation, Attraction Mechanism and F-Test Studies

The metformin (MET) in wastewater has raised concerns about potential environmental impacts. This study aimed (i) to increase MET removal by modifying surface of nutshell based activated carbon using Cu(II) salt (Cu-NSAC), (ii) to perform F-test to verify the significance of variances by comparing the linear method (L-M) and the non-linear method (NL-M), in the quest to solve isotherm together with kinetic models, and (iii) to utilize Polymath mass transfer (PMT) model for simulation purpose to guess the Cu-NSAC’s mesopores surface area (MESO-SA). The Cu-NSAC adsorbed higher MET of 8.67 mg/g as compared to pristine NSAC with 6.13 mg/g. In terms of adsorptive BET (Brunauer-Emmet-Teller) surface area (BET-SA), the value for Cu-NSAC was 911.13 m2/g. The adsorption process obeyed Langmuir and pseudo-second order (PSO) models, as revealed by L-M and NL-M. Langmuir single-coverage uptakes, Qm was 13.70 mg/g (L-M) as well as 13.55 mg/g (NL-M). In the F-test, the null hypothesis, Ho stated that the variances of both methods were equal. According to the decision rule (if F > F critical ⇒ reject Ho; if F < F critical ⇒ accept Ho), all computed F values were smaller than F critical (5.05). Therefore, Ho was accepted, indicating that both L-M and NL-M yielded statistically similar variances for all models. Simulating PMT model demonstrated strong predictive accuracy, estimating a MESO-SA of 573.02 m2/g compared to the actual measurement (614.52 m2/g), with a resulting error of 6.75%. Uptakes of MET by pristine NSAC was assisted by dipole–dipole and hydrogen bonds only, whilst adsorption of MET onto Cu-NSAC was enhanced by additional ion–dipole bond.