Biopolymer composites are known for their utility in diverse applications. In this paper, we report an effective methodology for the detoxification of chromium using cellulose-montmorillonite composite material as the adsorbent. The interaction of surfactant modified sodium montmorillonite (NaMMT) with cellulose biopolymer is followed by the subsequent adsorption of Cr(VI) from aqueous solution as bichromate anion onto the surface of the biocomposite material. The composite adsorbent was characterized comprehensively using Fourier transform infrared spectroscopy (FT-IR), Energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD) and Branauer-Emmett-Teller (BET) isotherm studies. The material exhibited a maximum adsorption capacity of 22.2 mg g–1 in accordance with the Langmuir isotherm model. The mesoporous nature of the material was ascertained from the nitrogen adsorption isotherm study and the adsorption process was in accordance with second order kinetics. The spontaneity of the adsorption process could be confirmed from the study of the adsorption thermodynamics. The composite material could be regenerated using sodium hydroxide as the eluent. The adsorbent could be reused with quantitative recovery for 10 adsorption–desorption cycles. An aqueous phase feed volume of 400 mL could be quantitatively treated by column method at 100 mg L–1 concentration of Cr(VI) with a preconcentration factor of 50. The applicability of the method is demonstrated in the quantitative removal of total chromium from a chrome tannery effluent sample.

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Graphite-like graphitic carbon nitride (g-C 3 N 4 ) has gained considerable interest in the past few years. However, merely a few studies have been undertaken regarding the application of g-C 3 N 4 for metal adsorption and visible-lightdriven reduction of aromatic nitro compounds. Here, we describe a versatile method for the preparation of g-C 3 N 4 nanocomposite decorated with magnetite nanoparticles (g-C 3 N 4 @Fe 3 O 4 NPs) that subsequently showed their efficiency in sequestration of Cr(VI)/Cr(III) and NaBH 4 -mediated conversion of 2-nitroaniline (2-NA) and 4-nitroaniline (4-NA) under visible-light exposure. The as-synthesized g-C 3 N 4 @Fe 3 O 4 NPs adsorbent revealed excellent water dispersibility, superior magnetic property, and porous structure. Numerous surface hydroxyls (−OH) and amino groups (−N, −NH, −NH 2 ) enabled g-C 3 N 4 @Fe 3 O 4 NPs to rapidly isolate Cr(VI) from aqueous solution through applying an outer magnetic field. The adsorbed Cr(VI) on the g-C 3 N 4 @Fe 3 O 4 NPs surface offered a maximum equilibrium adsorption capacity of 555 mg g −1 , and their absorption behavior followed the Langmuir isotherm and pseudo-second-order kinetics model. The morphology, surface properties, crystalline structure, and chemical compositions of g-C 3 N 4 @Fe 3 O 4 NPs were thoroughly investigated. In real-world applications, g-C 3 N 4 @Fe 3 O 4 NPs was implemented for the determination of total chromium in industrial soil sludge samples. Additionally, NaBH 4 -induced reduction of 2-NA to 2-aminoaniline and 4-NA to 4-aminoaniline catalyzed by g-C 3 N 4 @ Fe 3 O 4 NPs (catalyst loading as low as 20 mg) was achieved within 8 min.