Adsorption of Rare Earths(Ⅲ) Using an Efficient Sodium Alginate Hydrogel Cross-Linked with Poly-γ-Glutamate

<div><p>With the exploitation of rare earth ore, more and more REEs came into groundwater. This was a waste of resources and could be harmful to the organisms. This study aimed to find an efficient adsorption material to mitigate the above issue. Through doping sodium alginate (SA) with poly-γ-glutamate (PGA), an immobilized gel particle material was produced. The composite exhibited excellent capacity for adsorbing rare earth elements (REEs). The amount of La³⁺ adsorbed on the SA-PGA gel particles reached approximately 163.93 mg/g compared to the 81.97 mg/g adsorbed on SA alone. The factors that potentially affected the adsorption efficiency of the SA-PGA composite, including the initial concentration of REEs, the adsorbent dosage, and the pH of the solution, were investigated. 15 types of REEs in single and mixed aqueous solutions were used to explore the selective adsorption of REEs on gel particles. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy analyses of the SA and SA-PGA gel beads suggested that the carboxyl groups in the composite might play a key role in the adsorption process and the morphology of SA-PGA changed from the compact structure of SA to a porous structure after doping PGA. The kinetics and thermodynamics of the adsorption of REEs were well fit with the pseudo-second-order equation and the Langmuir adsorption isotherm model, respectively. It appears that SA-PGA is useful for recycling REEs from wastewater.</p></div

Adsorption isotherms of La³⁺ and Ce³⁺ on SA-PGA gel particles.

<p>Adsorption isotherms of La³⁺ and Ce³⁺ on SA-PGA gel particles.</p

Assignment of the main vibrational modes.(C_HCl:0.1mol/L,50mL).

<p>Assignment of the main vibrational modes.(C_HCl:0.1mol/L,50mL).</p

Selective adsorption experiments of REEs: (a) single solution, (b) mixed solution.

<p>Selective adsorption experiments of REEs: (a) single solution, (b) mixed solution.</p

Digital photographs of SA gels (a, b, c, d) and SA-PGA gels (e, f, h, i).

<p>Digital photographs of SA gels (a, b, c, d) and SA-PGA gels (e, f, h, i).</p

Effects of the initial concentration of REEs, adsorbent dosage, and pH of solution on the adsorption by gel particles (Adsorption conditions: temperature 30°C; 150 rpm; and 3h adsorption time).

<p>Effects of the initial concentration of REEs, adsorbent dosage, and pH of solution on the adsorption by gel particles (Adsorption conditions: temperature 30°C; 150 rpm; and 3h adsorption time).</p

Adsorption kinetic curves (a) and pseudo-second-order plots (b) for the adsorption by gel particles.

<p>Adsorption kinetic curves (a) and pseudo-second-order plots (b) for the adsorption by gel particles.</p

Regeneration of these two gel particles (Adsorption conditions: 30 ml of 0.05 M hydrochloric acid solution, 30 min, 150 rpm, 30°C).

<p>Regeneration of these two gel particles (Adsorption conditions: 30 ml of 0.05 M hydrochloric acid solution, 30 min, 150 rpm, 30°C).</p

FT-IR spectra of SA, PGA, SA-PGA, SA-PAG-La, and SA-PGA-La-HCl gels.

<p>FT-IR spectra of SA, PGA, SA-PGA, SA-PAG-La, and SA-PGA-La-HCl gels.</p

Conjugation-Grafted-TiO₂ Nanohybrid for High Photocatalytic Efficiency under Visible Light

Abundant and renewable solar light is an ideal resource for the industrial application of TiO₂ photocatalysis in environmental purification. Over the past decades, the pursuit for visible-light photocatalysts with low cost, simple process, and high efficiency remains a challenging task. Here, we report a novel organic–inorganic nanohybrid photocatalyst (conjugation-grafted-TiO₂) by chemically grafting conjugated structures onto the surfaces of TiO₂ nanoparticles through controlled thermal degradation of the coacervated polymer layer. The interfacial C–O–Ti bonds between TiO₂ and conjugated structures can act as the pathway to quickly transfer the excited electrons from conjugated structures to TiO₂, therefore contribute to high visible-light photocatalytic efficiency. Our findings provide an economic route to prepare the conjugation-grafted-TiO₂ nanohybrid, and develop a routine to improve the photocatalytic efficiency of organic–inorganic hybrid materials through the interfacial interaction