Highly synergic adsorption and photocatalytic degradation of walnut shell biochar/NiCr-layered double hydroxides composite for Methyl orange

Abstract

Methyl orange (MO) is a kind of azo dye, and will do great harm to the ecological environment. Alleviating this problem by removing MO is crucial role to prevent harmful damage to the environment. In this paper, NiCr layered double hydroxides (LDH) were prepared through hydrothermal method and then modified with different mass rations of walnut shell biochar. The structure and properties of biochar/NiCr-LDH composites were analyzed by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) coupled with energy disperse spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Moreover, the adsorption and photocatalytic degradation behavior of composites on anionic dye MO were investigated. Characterization results indicated that NiCr-LDH was perfectly synthesized and coated on the biochar. All the biochar/NiCr-LDH composites show enhanced adsorption and photodegradation performance for MO dye compared with pure NiCr-LDH and biochar. When the biochar content was 22.3 wt.% and the biochar/NiCr-LDH (S2) dosage was 1.0 mg/mL, the maximum removal amount of MO could reach 100 % within 60 min at the natural pH, experimental data fitted well with the pseudo-second-order kinetic and Freundlich isotherm model, and the maximum adsorption capacity of S2 was 108.2 mg/g. Besides, compared with NiCr-LDH, S2 also demonstrated wonderful photodegradation activity for MO under visible-light irradiation, the rate constant of S2 (0.0173 min−1) is about 1.5 times that of NiCr-LDH (0.0118 min−1), and the enhanced performance can be due to the faster separation of electron-hole pairs, in which biochar acted as charge separation carriers. Meanwhile, the hydroxyl radical and superoxide radical played crucial roles in the dye photocatalytic degradation, and a possible photocatalytic degradation mechanism was proposed. The excellent photocatalytic activity and stability make biochar/NiCr-LDH an ideal photocatalyst to solve environmental crisis.