Adsorptive removal of Methylene Blue and Congo Red by utilising wheat straw

The study investigated the adsorption of Methylene Blue (MB) and Congo Red (CR) dyes from a solution using Wheat Straw (WS), an adsorbent. The WS surface contained OH and other functional groups, and its pHpzc value was 6.7. The optimal pH for MB adsorption was 8–9, and for CR adsorption, it was 5–6. The kinetics of MB and CR dye adsorption onto WS were evaluated using pseudo-first-order, pseudo-second-order kinetic models, Elovich model, intra-particle, and liquid film diffusion models. The data were best fitted to pseudo-first-order kinetics. The maximal removal percentage for MB was 89.5% at 293 K with an adsorbent dose of 0.2 g and an interaction time of 30 minutes. And the Langmuir adsorption capacity (Qmax) was recorded to be 34.27 mg/g for MB. For CR, the maximal removal percentage was 76.7% at 293 K with an adsorbent dosage of 0.1 g and a contact time of 40 minutes. And the Langmuir adsorption capacity (Qmax) was recorded to be 35.07 mg/g for CR. The reaction was exothermic and spontaneous. After five cycles of adsorption and desorption, the percentage removal of MB decreased from 89.580% to 50.970% and CR dye from 76.053% to 36.341%. The study concluded that WS is an economical and environmentally friendly adsorbent for removing cationic and anionic dyes from solutions.