Lignocellulosic-derived modified agricultural waste: Development, characterisation and implementation in sequestering pyridine from aqueous solutions

• H3PO4 modified agricultural waste (MAW) is explored as an adsorbent.
• Optimum pyridine removal at pH 6, adsorbent load of 5 g L−1 and contact time of 5 h.
• Obtained high adsorptive uptake of pyridine in comparison with other adsorbents.
• Adsorption mechanism involves electrostatic and π–π dispersive interactions.
• Spent adsorbent is regenerated and reused for five adsorption–desorption cycles.

The development and characterisation of modified agricultural waste (MAW) by H3PO4 activation is addressed in this study for sequestering pyridine from aqueous solutions. The adsorbent is characterised by carbon, hydrogen and nitrogen content of 55.53%, 3.28% and 0.98% respectively. The adsorbent also shows acidic (carboxylic, lactonic, phenolic groups) and basic carbon surface functionalities, functional groups viz. hydroxyl, carboxylic acid and bounded water molecules, BET surface area of 1254.67 m2 g−1, heterogeneous surface morphology and graphite like XRD patterns. Adsorption of pyridine is executed to evaluate the adsorptive uptake in batch (qe = 107.18 mg g−1) as well as in column system (qe = 140.94 mg g−1). The adsorption process followed the pseudo-second-order kinetics with the Langmuir isotherm best representing the equilibrium adsorption data. The thermodynamic parameters (ΔHo = 9.39 kJ mol−1, ΔGo = −5.99 kJ mol−1, ΔSo = 50.76 J K−1 mol−1) confirm the endothermic and spontaneous nature of the adsorption process with increase in randomness at solid/solution interface. The adsorption mechanism is governed by electrostatic and π–π dispersive interactions as well as by a two stage diffusion phenomena. Thermally regenerated spent MAW exhibited better adsorption efficiency for five adsorption–desorption cycles than chemically regenerated. The low-cost of MAW (USD 10.714 per kg) and favourable adsorption parameters justifies its use in the adsorptive removal of pyridine.

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