Adsorption of acid violet 90 dye onto activated carbon and guava seed powder adsorbents

Powdered activated carbon (PAC) and guava (Psidium guajava L.) seed powder (G-seed), were used as adsorbents for the adsorption of acid violet 90 (AV90) dye from simulated wastewater. Both adsorbents were thoroughly characterized using a variety of instrumental techniques. The FTIR result confirmed that both adsorbents contain hydroxyl, - OH, carboxyl, C = O and ether, C-O-C groups, however, the number of the surface oxygen complexes on the PAC in comparison with that of the G-seed was diminished. The presence of oxygen-based groups was further confirmed by the EDX analysis. Compared to the G-seed's BET surface area of 38.25 m(2)/g, the PAC had a high value of 804.46 m(2)/g with superior sorption potentials. The optimal adsorption was established at pH 2.0 and 0.2 g/L adsorbent concentration for both adsorbents. Also, the experimental isotherm data for G-seed and PAC fit the Freundlich model well, indicating physisorption interaction on heterogeneous sites. Pseudo-first-order (PFO) and pseudo-second-order (PSO) models successfully described the kinetic data for G-seed and PAC, respectively. Notably, the PFO and PSO's satisfactory fittings imply the occurrence of elementary reversible sorption and physisorption interaction, respectively. A mixed adsorption mechanism that incorporates pore filling, hydrogen bond formation, electrostatic interactions, and n-pi interaction was also suggested. The study, therefore, shows that the G-seed exhibit a better overall adsorption performance in terms of the cost of adsorbent per gramme of the adsorbate removed. Hence, it can be successfully used as a cheap adsorbent for the treatment of AV90 dye-waste water.