Adsorption of Rhodamine B from an aqueous solution by acrylic-acid-modified walnut shells: characterization, kinetics, and thermodynamics.

A batch experiment was used in studying the effect of acrylic-acid-modified walnut shell (MWNS) as a low-cost adsorbent for removing Rhodamine B (RB) cationic dye in aqueous solutions. The adsorbent dosage, initial dye concentration, contact time, temperature, pH, and supporting electrolyte concentration on the adsorption behaviour of the adsorbent were explored. The adsorbent was characterized using the point of zero charge (pHPZC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), automatic specific surface analysis (BET), and X-ray photoelectron spectroscopy (XPS). Results showed that MWNS had abundant active groups and rough surface, which is conducive to the adsorption process. The kinetics and equilibrium data of MWNS-to-RB adsorption were in accordance pseudo-second-order kinetic and Freundlich isotherm models, respectively. Under optimal adsorption conditions, the maximum adsorption capacity of RB was 48.87 mg·g-1. Thermodynamic results showed spontaneously and exothermically the adsorption process. Moreover, the addition of electrolyte had a negative effect on equilibrium adsorption capacity and adsorption rate.HIGHLIGHTS Acrylic-acid-modified walnut shells was used as an adsorbent for the removal of Rhodamine B (RB).The adsorption of RB by modified walnut shells was greatly affected by pH.Pseudo-second-order kinetic and Freundlich model fit the experimental data.The modified walnut shell can remove RB through electrostatic attraction, hydrogen bonding, and electron donor-acceptor interaction.

Synthesis of a functional biomass lignin-based hydrogel with high swelling and adsorption capability towards Acid Red 73.

In this study, sodium lignosulfonate (LS) was used as raw material. Acrylamide (AM) and acryloxyethyltrimethylammonium chloride (DAC) were grafted onto LS through the free radical graft copolymerisation to synthesise a functional biomass terpolymer lignin-based hydrogel adsorbent (LAD). The effects of different factors on the LAD adsorption of Acid Red (AR 73) were investigated through the static adsorption method. LAD adsorbed AR 73 (C0=100mg·L-1) for 2 h to reach equilibrium, and the equilibrium adsorption capacity and removal rate were 47.59 mg·g-1 and 95.18%, respectively. The prepared LAD hydrogel swelling ratio for 2 h was 25 g·g-1, and the water loss rate in ethanol solvent in 120 min was 93.51%. The adsorption of AR 73 by LAD was consistent with the Langmuir isotherm adsorption model. This adsorption was a single-molecule adsorption with a maximum adsorption capacity of 409.84 mg·g-1. The adsorption was a process of spontaneous heat release and entropy reduction. The adsorption kinetic was in accordance with the pseudo-second-order model, and the adsorption activation energy was 2.501 kJ·moL-1. Moreover, the mechanism of adsorption was electrostatic attraction, and comprehensive effects of physical, and chemical adsorption and hydrogen bond. The LAD hydrogel adsorbent has a remarkable adsorption effect on AR 73, and can be used as an efficient and recyclable biomass adsorbent for the treatment of anionic dye wastewater.