A Prussian blue analog-based copper-aluminum layered double hydroxide for cesium removal from water: fabrication, density functional theory-based molecular modeling, and the adsorption mechanism

A new type of adsorbent, a Prussian blue analog-based copper-aluminum layered double hydroxide (PBA@CuAl-LDH), was successfully synthesized using a one-step method for the removal of radioactive Cs+ from wastewater. The adsorption performance, characteristics and the underlying adsorption mechanism of PBA@CuAl-LDH were systematically examined. The results showed that PBA@CuAl-LDH exhibited excellent adsorption performance, with a maximum adsorption capacity of 109.2 mg g-1. Over 85% of PBA@CuAl-LDH can be recycled, and the material exhibited only a 6.6% loss in adsorption performance. The adsorption process was well-fitted using the pseudo-second-order kinetic model and the Freundlich isotherm model, revealing the surface heterogeneity of the composite adsorbent. A molecular model of PBA@CuAl-LDH was constructed by combining density functional theory and multiple instrumental characterization techniques. Our results indicate that PBA crystals can be generated between layers and on the surface. Ion exchange was revealed as the main adsorption mechanism of Cs+ by PBA@CuAl-LDH. Specifically, the interstitial spaces of the PBA crystals generated between the layers and on the surface played an important role in ion exchange. These findings provide concrete theoretical support for radioactive pollution control and have significant value in directing the fabrication of cesium removal materials and their future engineering application.

Synthesis of Prussian blue-embedded magnetic micro hydrogel for scavenging of cesium from aqueous solutions; Batch and dynamic investigations

A magnetic micro porous structure composite based on alginate and Prussian blue (M-SA-PB) was simply prepared for cesium removal from the aqueous solutions. The gelation and formation of PB proceeded through the same step, which made the PB homogenously distributed and firmly attached to the alginate matrix. The homogenizer was applied to break down the bulky gel structure into micro-ones, and the lyophilizer will provide the porous structure. Batch cesium sorption experiments showed that the adsorption kinetics and isotherms were attributed to the pseudo-second-order model and Langmuir isotherm. Moreover, the Cs-ion is favorably adsorbed on the M-SA-PB composite surface as a monolayer towards Cs, with a maximum adsorption capacity reach of 191.0 mg/g. Furthermore, the M-SA-PB adsorbent showed excellent adsorption selectivity of Cs from multiple-ion solutions. Our work was extended to use the M-SA-PB composite in dynamic cesium sorption. The column studies showed that the removal efficiency of Cs+ increased with increasing bed depth as well as the initial cesium concentration. Finally, as previously mentioned, the M-SA-PB could be considered an excellent Cs+ scavenger employing both batch and dynamic approaches, which makes it a promising adsorbent for practical investigations.

Highly selective adsorption and lattice process of cesium by cubic cyanide-based functional materials

Cesium (Cs) is a byproduct of nuclear bombs, nuclear weapons testing, and nuclear fission in nuclear reactors. Cs can enter the human body through food or air and cause lasting damage. Highly efficient and selective removal of ¹³⁷Cs from low-level radioactive effluents (LLREs), which contain many radionuclides and dissolved heavy metal species, is imperative for minimizing LLRE volume, and facilitating their final disposal. Prussian blue analogs (PBAs) have received much attention as materials for the removal of radioactive Cs because of their affinity for adsorbing Cs⁺. In this study, an inexpensive and readily available cyanide-based functional material (PBA_Cu) exhibiting high efficiency and excellent selectivity toward Cs capture was designed through a facile low-temperature co-precipitation process. Nano-PBA_Cu, crystallizing in the cubic space group (Fm-3m (225)), has an average pore size of 6.53 nm; consequently, PBA_Cu can offer abundant atomic occupation sites for capturing and incorporating Cs. Here, the pseudo-second-order kinetic model and Langmuir model fitted well with the adsorption of Cs ⁺ on PBA_Cu, with a maximum capture capacity of 95.75 mg/g within 5 min, confirming that PBA_Cu could rapidly capture Cs ions. PBA_Cu strongly and selectively interacted with Cs even in a simulant containing large Na⁺, NH₄⁺, Ca²⁺, and Mg²⁺ ion concentrations in an aqueous solution. The process of Cs ⁺ adsorption by cyanide-based functional crystals was confirmed to involve the entry of Cs⁺ into cyanide-based functional crystals to replace K⁺ and finally achieve the lattice incorporation of Cs. The current results broaden the lattice theory of radionuclide Cs removal and provide a promising alternative for the immobilization of Cs from radioactive wastewater.

Prussian blue analogs-based layered double hydroxides for highly efficient Cs+ removal from wastewater

In this work, novel Prussian blue analogs-based layered double hydroxide (PBA@ZnTi-LDH) was in situ synthesized and used for radioactive Cs⁺ removal from wastewater. The results suggested that this PBA@ZnTi-LDH prepared using LDH as skeleton and transition metal source showed higher adsorption capacity (243.9 mg/g) and water stability than conventional PBAs, and promising application in scale-up Cs⁺ removal. Thus, it was granulated by calcium alginate and the PBA@ZnTi-LDH/CaALG exhibited favorable post-separation and fixed-bed adsorption ability at different Cs⁺ concentrations and flow rates, highlighting its application perspective on Cs⁺ removal from various kinds of wastewater. Moreover, the real-world Cs⁺ removal was preliminarily explored using natural complex Cs⁺-containing water. As a result, this stable and easily separated PBA@ZnTi-LDH/CaALG showed high removal efficiency, selectivity and good reusability, which was promising in scale-up Cs⁺ removal from the real-world wastewater.

Enhanced kinetics and super selectivity toward Cs+ in multicomponent aqueous solutions: A robust Prussian blue analogue/polyvinyl chloride composite membrane

Developing effective adsorbents for ¹³⁷Cs removal from complex wastewater systems has been a significant challenge. Although existing spheres adsorbents could improve the post-separation ability and practical operability, the adsorption kinetics are still significantly retarded due to the large intra-particle diffusion resistance. Here, we demonstrate the efficiency of a robust Prussian blue analogue/polyvinyl chloride composite membrane (PPM), which was easily prepared by a simple solvent evaporation method. In virtue of the less dense layer and ion-sieving functionality, it showed enhanced kinetics (5 h) and super selectivity (S_F = 248.3-5388.6) towards Cs⁺. New PPM was robust within a wide pH range (2-10) and exhibited favorable removal capacity (152.8 mg/g), placing it at an outstanding material for Cs⁺ removal among other adsorbents. Moreover, PPM could be simply eluted and reused using a KCl solution as eluent. A study of the adsorption mechanism confirmed an ion-exchange action during the removal process. Thus, PPM is considered to be a promising candidate for the removal of Cs⁺ from multicomponent aqueous solutions.

Robust and recyclable sodium carboxymethyl cellulose-ammonium phosphomolybdate composites for cesium removal from wastewater

A novel, facilely prepared, recyclable sodium carboxymethyl cellulose-ammonium phosphomolybdate composite (CMC-AMP) was synthesized by chemical cross-linking and used for Cs+ removal. The effects of adsorbent dosage, pH value, initial Cs+ concentration, contact time, temperature and competitive ions on adsorption were investigated. The results showed that CMC-AMP with good mechanical properties could effectively adsorb Cs+ in a wide pH range. In addition, the adsorption process of CMC-AMP was better fitted with the Lagergren first-second model and Langmuir isotherm model. Furthermore, CMC-AMP can be reused five times using ammonium chloride as the eluent without an obvious decrease in absorption activity. The results reveal that CMC-AMP can be used as a low cost and recyclable Cs+ adsorbent.