Experimental design via NaOH activation process and statistical analysis for activated sugarcane bagasse hydrochar for removal of dye and antibiotic

Abstract

In this study, hydrochar derived from SB was activated with sodium hydroxide (NaOH) by the cold alkali activation method, to increase the number of oxygenated functional groups, as well as enhance its porosity by clearing pore blockages. Response surface methodology by central composite design (RSM-CCD) was employed to investigate the effects of NaOH activation process parameters (NaOH concentration (A), hydrochar mass ratio (B) and activation time (C)) on prepared hydrochar towards three responses; activated hydrochar (AHC) yield, tetracycline (TC) antibiotic removal and crystal violet (CV) dye removal. Through the analysis of variance (ANOVA) tests, the significance sequences of single factor affecting were B > C > A for AHC yield, A > B > C for both TC removal and CV removal. However, the significant interaction effect for both AHC yield and TC removal was observed with BC only. Meanwhile, CV removal was noticed with different result whereby two significant interaction effects (AB and AC) were observed. Through optimisation study, optimised AHC (AHCop) was generated by maximising all three responses and it was predicted to generate 54.23% yield with TC and CV adsorption capacity of 22.60 mg g−1 and 47.97 mg g−1. A relative standard deviation (R.S.D) of 1.32%, 0.97% and 2.14% (n = 3) were obtained for AHC yield, TC and CV removal, respectively. Following optimisation, AHCop was characterised by N2 adsorption-desorption isotherm analysis, Field Emission Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, and Thermogravimetric analysis. In brief, the physiochemical characteristics of AHCop were observed with meso and macro pore structures, numerous microsphere-like particles with crack surfaces, abundance functional groups, strong π-π reaction and high thermal stability. The optimisation study was succeeded to develop AHCop at a higher yield and remove both TC and CV at higher adsorption capacity compared to before activation.