Removal of methyl orange (MO) from aqueous solution using cationic surfactants modified coffee waste (MCWs)

• Coffee waste was modified with cationic surfactant for adsorptive removal of methyl orange from water.
• Adsorption of methyl orange onto MCWs was pH dependent.
• The amount of methyl orange decreased slightly with increase in the ionic strength of solution.
• Adsorption mechanisms mainly involve electrostatic interactions and hydrophobic interactions.
• The exhausted MCWs can be regenerated by 0.01 M NaOH solution.

In this present work, a commercial coffee waste was treated using cationic surfactants cetyltrimethyl ammonium bromide (CTAB) or cetylpyridinium chloride (CPC) to enhance its adsorption capacity for the removal of methyl orange dye (MO, anionic dye) from aqueous solutions. A series of experiments were undertaken in an agitated batch to assess the effect of key parameters such as pH, contact time, adsorbent dose and ionic strength. Maximum methyl orange dye adsorption onto modified commercial coffee waste (MCWs) was observed at pH 3.5 with 0.1 g/50 ml of adsorbent dose. Modeling study shows that pseudo-second-order kinetic model and Langmuir adsorption isotherm model provide better fitness to the experimental data. The maximum adsorption capacity (62.5 mg/g at 25 °C) was obtained with CPC modified commercial coffee waste. Calculated thermodynamic parameters ∆G0, ∆H0 and ∆S0 showed that adsorption is spontaneous and exothermic. The FT-IR analysis showed that possible mechanisms controlling MO adsorption on the MCWs included electrostatic interactions and hydrophobic interaction.

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