Superior dye degradation and adsorption capability of polydopamine modified Fe₃O₄-pillared bentonite composite

Owing to the increasing demand of environmentally benign materials for the degradation of hazardous dyes, herein we are reporting two different synthesis approaches for the fabrication of iron loaded bentonite composites by modifying and activating bentonite surface with polydopamine (PDA) followed by pillaring with Fe³⁺ (Fe-PDA-bentonite) and Fe₃O₄ (Fe₃O₄-PDA-bentonite). Both the composites were assessed for their adsorption and degradation performance using crystal violet (CV), Rhodamine B and Brilliant blue dyes following adopting advanced oxidation process type Fenton reaction under variable energy sources (Sunlight, UV light and Ultrasonication), concentration of H₂O₂ and catalyst dosage. Under UV light irradiation, the composites achieved complete degradation of the dyes within 60 min and showed degradation rate constant of 30.5E-3-81.8E-3. Textural characterizations of the composites were achieved via XRD, FTIR, TGA, XPS, SEM-EDX, TEM, N₂ adsorption, VSM and UV/Vis spectrophotometry. The adsorption data of CV over the two composites fitted well with Langmuir adsorption isotherm, exhibiting the maximum adsorption capacity of 862 mg/g and 1235 mg/g for Fe-PDA-bentonite and Fe₃O₄-PDA-bentonite composites respectively. LCMS analysis of the post degradation products revealed that both the composites followed different degradation pathways and Fe₃O₄-PDA-bentonite showed superior photocatalytic performance by accomplishing complete dye degradation without leaving any degradation products. FTIR analysis of the post-degradation composites confirmed their structural stability with negligible iron leaching. This study, accredited to its cost-effectiveness, ease of operation and high efficiency, provides useful reference information for the degradation of dyes on industrial level.