Removal of Congo Red and reactive black 5 dyes from aqueous solution using polyethylenimine-modified coffee waste adsorbent

The industrial wastewater especially from textiles industry contain high concentration of dyes that could bring adverse health effect to the human and aquatic life. In past researches, it has been shown that coffee waste is a potential adsorbent for cationic dye in comparison to anionic dye. Thus, in this study, polyethyleniminemodified coffee waste (PEI-CW) was synthesized through crosslinking reaction to evaluate its use as a potential adsorbent in removal o f hazardous anionic Congo Red (CR) and Reactive Black 5 (RB5) dyes from aqueous solution. The type of characterizations that were conducted on the adsorbent are FTIR, BET, BJH and XRD analysis. The presence of substantial amine group on PEI-CW was confirmed through FTIR analysis. The BET and BJH analysis showed a decrement in surface area and total pore volume of CW along with an increase in pore diameter after modification with PEI. The XRD analysis showed there is no obvious difference in crystalline structure of CW after being modified with PEI. Through batch adsorption experiment, PEI-CW has been proven to be a potential adsorbent due to 99% removal of 50 mg/L CR and RB5 dye from aqueous solution. The optimum parameter for CR dye aqueous solution is 60°C, pH 3, 0.1 g PEI-CW and 120 minutes. Whereas, for RB5 dye adsorption, the optimum parameter is 25 °C, pH 7, 0.1 g PEI-CW and 60 minutes. Model-fitting study showed Langmuir adsorption isotherm and pseudo-second order kinetic model as a better fit for both CR and RB5 dyes adsorption process. From Langmuir model, the maximum adsorption capacity was found to be higher for RB5 dye adsorption, which is at 77.5194 mg/g compared to 34.3543 mg/g for CR dye. The thermodynamic analysis suggested that both CR and RB5 dyes adsorption process is physisorption, spontaneous and endothermic in nature. From this study, it is inferred that PEI-CW could be potential low-cost adsorbent in removal of anionic CR and RB5 dyes from the aqueous solution, although higher adsorption is observed towards RB5 than CR dyes.